the innervatio onf th heare t of crustacea . ii. stomatopoda.precisely 8-5 cm. thirty-two arteries...

The Innervation of the Heart of Crustacea.II. Stomatopoda.

By

J. S. AlexandrowiczLwow (Poland).

With Plate 31 and 13 Text-figures.

CONTENTS.PAGE

INTRODUCTOEY 511HISTORICAL 512MATERIAL AND METHODS 512DESCRIPTIVE 513

I. SOME DATA CONCERNING THE ANATOMY OF THE HEART IN

S Q U I L L A M A N T I S . . . . . . . 513

I I . GENERAL ARRANGEMENT OF THE NERVES SUPPLYING THE

HEART 517

1. Three Systems of Nervous Elements . . . 5172. General course of the Nerve-fibres in the Heart-wall . 518

I I I . LOCAL SYSTEM . . . . . . . . 520

IV. N B B V I CARDIACI DORSALES. SYSTEM OF REGULATOR NBRVES

OF THE HEART . . . . . . . . 528

1. General Arrangement . . . . . . 5282. Elements of the dorsal nerves in the ganglionic trunk 532

System I 534System I I 536

V. NERVES OP THE ARTERIAL VALVES . . . . . 539

1. Nervi segmentales cordis . . . . . 5392. Nervus cardiacus anterior . . . . . 5 4 1

DISCUSSION 542SUMMARY 546LITERATURE CITED 548

INTRODUCTOEY.

WHEN working out the innervation of the heart of theDecapod Crustacea—the subject of my previous publication1—I met some difficulties in making the preparations and in the

1 This Journal, vol. lxxv, Part II, 1932.

NO. 304 L 1

512 J. S. ALEXANDROWICZ

interpretation of the observed elements. I then turned to theStomatopods expecting to find there some enlightenment onseveral dubious questions, since the size and the shape of theheart in these animals as well as the position of the main nerve-trunk in this organ allowed one to hope that the investigationswould here be easier than in the Decapods. Though for variousreasons the nerve-system of the heart in the Stomatopods, too,could not be thoroughly analysed, and I am not fully satisfiedwith the obtained results, I proceed to give an account of myresearches.

HISTORICAL.Respecting the bibliography of the subject we may say that

few writers have paid attention to the heart-nerves of Stomato-pods. In 1883 C. Claus, when describing the circulatory systemin the larval form of these animals, noticed large nerve-cellslying on the heart-tube at regular intervals, each behind anostium. More precise observations are due to J. Nusbaum whorecorded them in 1899 in two papers, one published in Germanand the other in Polish, the latter somewhat more detailed andcontaining more figures. This writer described various fibresin the main trunk of the heart of Squ i l l a m a n t i s and addedsome remarks about the nerve-cells.

The same nervous trunk has been also seen and figured byPolice (1909).

MATERIAL AND METHODS.During my sojourn in Naples in 1930, thanks to the amiability

of Professor Dr. R. Dohrn, Director of the Zoological Station,I was provided with a sufficient quantity of large specimens ofS q u i l l a m a n t i s , and could begin my investigations. Themethods described in my previous paper, i.e. staining withmethylene blue and rongalit white, were chiefly used. Thestaining of the nervous elements in the heart was obtained bysubmerging the tissue in a solution of the dye, or by injectingit into the body of the living animal. The injection was made inthe abdomen from its ventral or dorsal side; in the latter casethe needle was introduced under the carapace between twosegments, and the dye pressed into the pericardial cavity. One

THE INNERVATION OF THE HEART OF CRUSTACEA 5 1 3

must be on one's guard during these manipulations, as theanimals use not only their claws but also the spines of the telsonas weapons of defence. One to six hours after the injection thedorsal part of the carapace with the adjacent muscles wasremoved and the heart exposed. Its main nerve-trunk, lyingsuperficially on the dorsal wall, could be observed withoutsectioning the heart and even without taking it out from thebody. Thus the heart can be left in s i t u till the stainingsucceeds.

In order to avoid shrinking of the heart-wall I employed aproceeding which had proved useful when making preparationsof the digestive tube of small animals, i.e. I introduced glasstubes of adequate calibre in the organ before fixation, and inthis way the heart remained stretched in the fixing and washingfluids.

Besides the vital staining, I also employed the staining ofthe nerve-tissue by means of silver salts, viz. the method ofCajal in the modification of Schultze and that of Bielschowskymodified by Gross. The description of these methods as theyhad been used by me is to be found in my previous papersabout Cephalopods ('Arch, de Zool. exp. et gen.' 66, 1927).The results obtained with Squ i l l a are not bad, but in manypreparations the impregnation of the connective tissue hindersthe observation of nerve elements.

DESCRIPTIVE.

I. SOME DATA CONCERNING THE ANATOMY OF THE HEART

IN S Q U I L L A M A N T I S .

The circulatory system of the Stomatopoda had been describedand figured in the works of Milne-Edwards (1834), Claus (1883),and Giesbrecht (1913). The figure showing the heart and thevessels in Squ i l l a m a n t i s given by Milne-Edwards is notquite exact. The representation adopted by Giesbrecht in hiswork about the anatomy of the Crustacea is based on the figureof Claus. As this writer had investigated' the larval form I thinkit not superfluous to give a view of the heart in an adult speci-men of Squ i l l a mantis—the object of my investigations.

L l 2

514 J. S. ALEXANDEOWICZ

Text-fig. 1 shows the heart of S q u i 11 a, with all the arterieswhich arise from it. We see that it has the shape of a long tubeof unequal diameter. The anterior part presents a dilatationwhich is followed by a narrower part. In the next segments theheart-tube becomes wider again but its width diminishes towardsthe posterior end.

The length of the heart-tube is approximately equal to halfthe length of the body; thus in an animal 17 cm. long it wasprecisely 8-5 cm.

Thirty-two arteries arise from the heart. Two of them are theprolongation of the heart-tube in the median line, the others arepaired vessels running to the sides. The first pair has an antero-lateral direction, the two most posterior pairs, XIV and XV, runoutwards and backwards; the remaining twelve pairs (II toXIII) originate from the heart at a right- or slightly obliqueangle. In order to simplify the description we shall use the termanterior and posterior aorta for the two median vessels, and weshall indicate by the numbers I to XV the lateral arteries.1

Text-fig. 1 shows that the exit-points of these vessels are notregularly situated. The first pair of lateral arteries branchoff near the anterior aorta and at a certain distance from thesecond pair. The exit-points of the subsequent five pairs II-VIlie nearer, those of the following pairs VII-XIII farther fromone another. The last three pairs are again situated close toeach other, especially XIV and XV; the last pair branch offquite near to the posterior aorta.

In the figure given by Milne-Edwards in his ' Histoire Natur-elle des Crustaces' sixteen lateral vessels are represented. Itseems that this writer was not aware that the two anteriorthoracic arteries have a common trunk arising from the heart(our lateral artery II), and he has drawn by mistake bothbranches of this trunk as originating from the heart.

1 The nomenclature used by Giesbrecht is as follows:Aorta anterior is called aorta.Aorta posterior is called arteria dorsalis pleica.Lateral arteries are called:

pair I, arteriae laterales cephalicae.pairs II—VIII, arteriae thoracicae.pairs IX-XV, arteriae pleieae.

Nn ley

TEXT-FIG. 1.

A. General view of the heart of Squi l la m a n t i s from the dorsalside, aa, ap, anterior and posterior aorta; Tr gang, ganglioniotrunk; a, p, y, dorsal nerves; I, II, III, XIV, XV, lateral arteries.B. Nervous system of the arterial valves. The heart is seen fromthe ventral side. N card ant, Nervus cardiacus anterior; Nnseg,Nervi segmentales cordis.

516 J. S. ALBXANDROWICZ

All the arteries possess at their origin valves supplied withmuscle-fibres.

On the dorsal wall of the heart the ostial orifices are noticeable.Their shape and dimensions can well be seen on the micro-photograph in Text-fig. 2. The first pair of ostia is situatedbetween the first and the second pair of arteries (Text-figs. 1 A,and 4). According to the representation of Claus and Gies-brecht these ostia lie in the larval form just before the secondlateral arieries. If the figure of Claus be correct, the positionof these ostia in the larva would differ from their position in theadult form, as in the latter they lie nearer to the anteriorend.

The second pair of ostia lies in the vicinity of the fourth pairof arteries, the third near to the fifth, and so on, each successiveostium being situated in the neighbourhood of each pair ofarteries. In consequence, the last two pairs of ostial orifices lienear to each other. There are in all thirteen pairs of ostia. Theexistence of the last pair was denied by Claus, but they aresurely present.

The heart-tube is made up of muscle-fibres which are arrangedin two layers. The inner layer, much thicker, consists of fibreswhich turn in right-handed spirals. The muscle-bundles areinterconnected by anastomosing muscle-fibres which branch offat very small angles, and are therefore better seen when theheart-wall is distended. Upon this muscle-layer lies outwardlya second layer of fibres of smaller calibre which are arrangedin a much looser and more irregular network; the meshes ofthis network are elongated in an opposite direction to that ofthe inner layer, i.e. they turn in left-handed spirals. The twolayers are not independent from each other, as branches fromthe thicker inner layer of fibres deviate outwards to enter thesuperficial plexus. In the anterior and posterior parts of theheart and in the vicinity of the ostia the arrangement of thefibres is more complicated.

The muscular heart-tube is surrounded by a coat of connectivetissue. Several bundles of this tissue expanding from the dorsalside of the heart may be considered as the suspensory ligamentsof the heart.

THE INNEBVATION OF THE HEART OF CRUSTACEA 517

II. GENERAL ARRANGEMENT OF THE NERVES SUPPLYING

THE HEART.

1. Three Sys tems of Nervous E l e m e n t s .As was mentioned, Claus and Nusbaum have stated that the

heart of the Stomatopoda is accompanied by a nervous trunkcontaining ganglionic cells. I have confirmed the discovery ofthese "writers during my investigations and, moreover, I coulddistinguish in the heart of S q u i 11 a three systems of nervouselements homologous with those which have been described byme in Decapods, viz.:

(1) A local nervous system;(2) A system of regulator nerves connecting the heart with

the central nervous system (Nervi c a r d i a c i dor-sales);

(3) A system of the nerves of the arterial valves.The local sys t em is made up of neurons, the cell-bodies

of which lie in the nerve-trunk running alongside the dorsalwall of the heart (Text-figs. 1 A, 2, and 3). The topography ofthis ganglionic trunk in Stomatopods is remarkable for thefact that it lies on the outside of the muscular fibres in the layerof the connective tissue enveloping the heart-tube, whereas inthe Decapoda this trunk is situated on the inner surface of themuscular tube, or, when partly covered with muscle-fibres, verynear to this surface. In Isopods I have found the ganglionictrunk on the inner side of the myocardium. Thus the Stomato-pods differ in this point from the two investigated groups ofCrustaceans, and, on the other hand, they have this superficialposition of the main trunk in common with the Xiphosura andwith the Scorpionidae.1

The sys tem of the r e g u l a t o r ne rve s consists ofthree pairs of nerves—Nervi cardiaci dorsales—which run fromthe central nervous system and join the ganglionic trunk ap-proaching the heart from its dorsal side. Text-figs. 1A, 4 A,

The third system—the ne rve s of t h e a r t e r i a l v a l v e s1 I have investigated the nerves of the heart in Euscorpius car-

pathicus, and intend to give a description in the future.

SIS J. S. ALEXANDROWICZ

—is made up of fibres which, being quite independent from thelocal system and from the regulatory nerves, take their coursedirectly to the valve-muscles of all the arteries arising from theheart, Text-fig. 1 B. We shall use the term Nervus cardiacusanterior (JV card ant) for the nerve supplying the valve of the

TEXT-FIG. 2.

Microphotographs showing the main nervous trunk (ganglionictrunk) of the heart, gc, ganglion cell; d, dendrites; Os, ostia.

anterior aorta, and Nn. cardiaci segmentales (Nn seg) for thenerves going to the remaining valves.

2. General course of the Nerve-fibres in theHear t -wa l l .

The main nervous trunk gives off branches of unequal lengthand character (Text-fig. 3):

(a) S h o r t b r a n c h e s of stout calibre, and richly ramified,lie in the neighbourhood of the ganglionic trunk. We shallreturn to them when speaking about the dendrites of the.ganglion cells (Text-figs. 2 A and 3, d.)

(b) Long branches arise from the ganglionic trunk at

THE INNBRVATION OF THE HEART OF CRUSTACEA 519

various angles and, while passing on the lateral and ventralwall of the heart, give off numerous dividing branches which

TEXT-FIG. 3.

Nerves of the dorsal wall of the heart, gc, ganglion cell; d, dendrites;a, fibre ending in the territory of another branch; Os, Ostia.

penetrate the heart-wall in its whole thickness. One part runsdeeper and distributes its terminal fibres between the innerlayer of the muscles; the other part takes a more superficialcourse and divides into thin branches in the connective tissue


enveloping the myocardium, and thence sends fibres to the outerlayer of muscles. Thus, all the muscle-fibres of the heart, thoseof the arterial valves excepted, are supplied with nerves fromthe ganglionic trunk. Whether or not the nerves also terminatein the connective tissue is difficult to ascertain, as incompletestaining can give rise to such images when a nerve-fibre does notreach the muscles and stops in the connective tissue.

When tracing the long branches we often find the areas ofdistribution of one branch overlapping the territory of neigh-bouring branches (Text-fig. 3, o); but the anastomotic junctionswhich are of common appearance in the Decapods are rare inStomatopods and seem to present accidental contacts of twofibres.

As a regular feature of the long branches arising from theganglionic trunk we must consider their being made up of fibresof unequal calibre. At many places there are two fibres runningparallel to each other both giving off dividing branches. How-ever, the two nerves cannot be traced up to the finer branches,and one does not meet with regular pictures of double innerva-tion such as may be observed in the skeletic muscles of variousArthropods. On the other hand more than two fibres, some-times three or four, may enter a nerve branching off from themedian trunk. Some data respecting the origin of these fibreswill be discussed further.

It will be noted that the majority of fibres making up themain trunk are nothing else than the axons of the ganglioniccells of the local system. The branches described above are theramifications of these axons.

With regard to the endings of the nerves on the muscles, Imust repeat my previous statements about the absence of anyspecial end-organs. In the methylene-blue preparations thenerves end, after many sub-divisions, as thin filaments which forthe most part break up in small beads.

III. LOCAL SYSTEM.

Gang l ion cells.—According to the observations of Clausthe nerve-cells are lying in the median trunk one in each seg-ment behind the ostial orifices; it should therefore be easy to

THE 1NNERVATI0N OF THE HEAET OF CRUSTACEA 521

ascertain their total number. As a matter of fact, this positionof the cells, indicated by Claus, can be found in the majority ofsegments; but difficulties arise when we turn to the anteriorand posterior parts of the heart. As we have seen, the situationof the ostia is here different and, moreover, nerve-cells arepresent where no ostia exist. Besides, the cells in the anteriorpart of the heart are smaller than in the farther segments andtheir staining is less satisfactory.

The Text-figs. 4 A and 4 B show the situation of the cells in theanterior and posterior part of the heart. In A the first two cells,gcv gc2, lie between the second pair of arteries, or a little posteri-orly between the second and the third pair. The first of thesecells, which is the smallest of all, can rarely be distinguished asit oftentimes has the aspect of an ovoid body which might beregarded as a swelling of the nerve. On the other hand, in somepreparations two similar bodies can be seen, and the suppositionas to the presence of another cell of equally small size might befound justifiable. However, as the cellular character of thissecond swelling could not be demonstrated I have omitted itin the drawing. The second ganglion cell lies near to the firstone, the third, gca, between the third pair of arteries. In thefollowing segments the ganglion cells can easily be found onebehind each pair of the ostia (Text-fig. 4 A, gc^; 4 B, §rc12_14).The cell gcu, corresponding to the fourteenth pair of arteries, liesoften rather between the ostial orifices than behind them. Thisis the last cell whose presence is beyond any doubt. In somecases I saw what might be regarded as a small cell between thelast (thirteenth) pair of ostia (Text-fig. 4 B, gc)?. As in this partof the heart leaf-like or cell-like masses often stain with methy-lene blue, I am compelled to express some doubts about the realexistence of this cell.

Putting all these observations together, we assume that thenumber of the nerve-cells is most probably fourteen and cer-tainly not greater than sixteen.

The size of the cells varies in different parts of the heart. Thefirst cell, the smallest, is ca 30/x; the following ones, i.e. thesecond, third, and fourth, are larger, 60 to 80p; the fifth, whichis at the same time more elongated than the foregoing, is

TEXT-FIG. 4.

A, anterior, and B, posterior, part of the heart of Squi l l a man t i s .Note the position of the ostia oslt os2, os12, os13, and of the ganglioncells ?c1_3, &c. The presence of the fifteenth cell gcf is douhtful;<*> jS. y> dorsal nerves.

THE INNERVATION OP THE HEART OF CRUSTACEA 523

ca 140/i. Then follow the largest cells of all, up to 180/x, but thelast ones are again a little smaller.

The size of the cells varies obviously with the size of thespecimens. All the given numbers have been obtained bymeasuring the cells of the same heart. In the figs. 1,2,3, PI. 31,the first, second, fifth, and eighth cell drawn from the samepreparation are represented.

The definition of the shape of the cells offers some difficulties.At a superficial observation all the cells, the four anteriorexcepted, look bipolar, with two stout processes arising from theopposite poles and running in the ganglionic trunk, but onmore careful examination one can find some cells sending off,besides the two named processes, one or two additional ar-borescent outgrowths (figs. 4 and 5, PL 31). The generalstructure of the cells, however, their symmetrical situation, thebehaviour of their long processes, do not give sufficient groundto distinguish various kinds of cells endowed with specialfunctions. This applies also to the four anterior cells, though theydiffer somewhat in their morphological character. The first celllooks as if it had a rounded shape. The next three cells have theaspect of pyriform elements with one process directed back-wards. However, this shape shown in the fig. 1, b, PI. 31, doesnot seem to render exactly the real form of the cells, as in somecases in better stained preparations more than one processarises from the cell (fig. 1, a, and 2, PI. 31). The nucleus of thecells, rarely noticeable, is comparatively larger than the nucleusof the ganglion cells in the heart of Decapods.

Nusbaum, in 1899, described and figured nerve-fibrils in theperipheral part of the cell-protoplasm: "Irn peripherischenTeile des Cytoplasmas findet sich ein zartes Fibrillennetz,welches den Kern umgiebt. . . ." As a matter of fact, the fibreswhich gave rise to this description can often be seen, but theydo not belong to the cell itself since they are given off by thebranches of the regulator nerves and only surround the cellswith a kind of basketwork (fig. 6, PL 31; Text-fig. 9). The cellsare embedded in a thick sheath of connective tissue which doesnot stain with methylene blue. Sometimes pale and indis-tinct fibres are noticeable which may be considered as belonging


to this sheath; in such cases the surface of the cells may appearuneven and of a somewhat spongy consistency (fig. 3, PL 81).

The proximal parts of the two main processes have an un-common structure, being made up of numerous fibres whichoriginate separately from the cell but unite at some distanceby twos or threes and finally make up one thick process. Asshown in fig. 7, PL 81, the exit-points of these fibres occupy agood part of the surface of the cell. Before the junction into thecommon trunk these roots may give off short branches runningto the sides (fig. 7, a, PL 31). Sometimes the different rootsdivide into two and unite again. Even the common trunk inits proximal part may be fenestrated in this way (fig. 7, J>,P1.31).

All these features can certainly neither be regarded as causedby an accidental cleavage of the fibres or be considered as deduc-tions from indistinct microscopical images, since these elementsare well delimited, and can be seen in many preparations pro-vided the methylene-blue staining of the nerves be not toodeep. In the latter case the processes appear as though theywere uniform up to the cells.

This interesting behaviour of the processes reminds onesomewhat of the structure of the cells in the spinal ganglia ofVertebrates, the peripheric parts of which are fenestrated, andsometimes the process of the cells looks as if it began withseveral roots.

In the majority of the cells, from the fifth to the fourteenthnamely, both processes have the same structure at their be-ginning. There is also no noticeable difference in their thicknessexcept in the fourteenth cell, the posterior process of which isthinner than the opposite one, whereas in the fifth cell theanterior process is perhaps a little thinner. But this differenceis not distinctly marked.

To each of the fourteen cells belong three kinds of projections:(a) short arborescences—the dendrites; (b) collaterals; and (c)long processes—the axons.

Dendr i tes .—We call dendrites as we did in our previouspaper, short arborescences arising from the main two processesand sometimes from the cell-body. They can originate atvarious distances from the cell, some in its vicinity, others at

THE INNBEVATION OF THE HEABT OF CRUSTACEA 525

a distance of 3 mm. or even more (fig. 11, PL 81). As to theirnumber I counted up to twelve such ramifications belongingto the same neuron. They are doubtless homologues of similaroutgrowths described in the Decapoda. In S q u i 11 a they areof various sizes and shapes (figs. 3-5, 7-11, PI. 31). Their trunkmay be longer or shorter, thinner or thicker. Sometimes thebush-like arborizations originate from the axon by means oftwo or three trunks (fig. 3, d, PL 31).

The characteristic ramifications of the dendrites end on themuscle-fibres (figs. 8 and 9, PL 31). The majority of the branchespass to the inner layer of the myocardium, but the superficialmuscle-bundles (fig. 8, ms, PL 31) receive some fibres too.

As in Decapods, the dendrites may be accompanied by thinaccessory fibres springing from the branches of the dorsalnerves (fig. 10, PL 31).

Col la tera ls .—We regard as collaterals the short and thinbranches arising from the axons and the proximal parts ofdendrites and ramifying in the ganglionic trunk (fig. 4, col,PL 31). It is difficult to ascertain, owing to their size andposition in this trunk, how numerous they are and how distantfrom the cell may be the collaterals sent by one axon. They endin fine networks of fibrils which enter into relation with thefibres of the dorsal nerves and perhaps also with collateralsof other axons.

Axons.—As we have pointed out in the chapter concerningthe general arrangement of the nerves in the heart-wall theaxons of the cells just described form the ganglionic trunk.There is no doubt that these axons give off long branchesrunning to the muscles, but in endeavouring to analyse theunits of this local system, i.e. to trace exactly the fibres of everyneuron, I failed in two important points.

Firstly, I could not make out how long the axons are, i.e. inwhich segment or segments a given cell has its terminal branches.The ganglionic trunk seems to be composed throughout itslength, the anterior and posterior part excepted, of five to sixaxons in each transverse section. Nevertheless, the tracing ofan axon at a longer distance has always been uncertain. To besure, the long branches of the axon do not arise in the same

526 J. S. ALEXANDBOWICZ

segment in which the dendrites are given off, but at a greaterdistance from the cell. The branches seen in Text-fig. 3 donot therefore belong to the cell represented in the same figurebut to a neuron the nucleated cell-body of which lies in one ofthe farther segments.1 But in which of them ? In some cases theaxon seemed to branch in the third segment counting from thecell in which it originated, but there is no evidence that all otheraxons behave in the same way. It is worthy of note that theterritory of the terminal branches of one neuron is evidentlynot confined to one segment only. This conclusion is drawnfrom the fact that side branches of two axons can be found inthe same segment of the heart. The fibres of different pro-venance may run independently to the muscles or can build upa common nerve. Even four fibres branching at the same placefrom different axons have been observed.

Secondly, there is no decisive evidence as to the character ofthe second thick process arising from the cell. As was pointedout, both the main processes are at their beginning seeminglyalike as to their mode of origin, their shape, calibre, and shortarborescences. One of these processes is surely the axon, butwhat is the other ? Is it to be considered as a second axon whichtakes its course in the opposite direction and branches in one ofthe segments lying on the other side of the cell as is hypotheti-cally represented in the diagram (Text-fig. 5 A)? Or is it com-pletely different from the axon, being only a thick trunk fromwhich dendrites arise as seen in the second hypothetical dia-gram (Text-fig. 5 B)? Its shape, and the behaviour of itsproximal parts, speak in favour of the first supposition; but thesecond one agrees better with the data obtained from theinvestigations of the same cells in Decapods. During myinvestigations on the nerve-cells in the heart of A s t a c u sf l u v i a t i l i s I have had as to the significance of their pro-jections the same doubts which are expressed here. But afterexamining the same elements in the marine Decapods I couldconvince myself that they had one axon and several dendrites,one of which was often thicker than the others. In the Stomato-

1 Under 'segment' is meant here that part of the heart which correspondsto the distance between two lateral arteries.

THE INNERVATION OF THE HEART OF CRUSTACEA. 527

«

TEXT-ITO. 5.

Explanation in text.

pods, too, the aspect of the four anterior and of the last posteriorcells conveys the impression that these cells possess one axononly. I am, therefore, inclined to think that this is the realstructure of the remaining cells also; but until the direct evi-dence be brought forward, i.e. until both processes can be traced

N O . 304 M m

528 J. S. ALBXANDEOWICZ

up to their ramifications, this statement is not indisputable.Another difficulty arises in determining the direction in whichthe axon is sent from the cells. As to the four anterior elementstheir axons run most probably backwards, whereas those of thetwo posterior cells run to the front; but where are directed theprocesses of the remaining cells ? We assume that one part ofthem runs forwards and the other backwards in some definedsequence. I have endeavoured to determine this direction bythe angles at which arise the branches. These observationshave but approximative value, since the branches may springfrom the same axon at various angles. It looks, however, asif the anterior part of the heart was innervated by the axonscoming from behind, and the posterior one by axons runningbackwards in the ganglionic trunk.

IV. NERVI CARDIACI DORSALES. SYSTEM OP EEGULATORNERVES OF THE HEART.1

. 1. Genera l A r r a n g e m e n t .

There are three paired nerves which run from the centralnervous system to the ganglionic trunk of the heart. Text-fig. 6 may facilitate orientation in the topography of the courseof these nerves. On the right side of this figure the tergite ispartly taken away in order to show the junction of the dorsalnerves with the ganglionic trunk, which takes place in the limitsof the fourth segment of the body. The skeletal parts of thissegment are described by Giesbrecht as follows: 'Das 4. Eumpf-segment hat ein weiches, durch eine quere Palte in 2 Wiilstegetheiltes Tergit, das von dem Hinterende des Ruckenschildesbedeckt wird. An der ventralen Seite ist es stark gepanzertund zwischen den Maxillipeden des 2.-5. Paares mit medianenKielen versehen.'

To this description I would add that this tergite containsparts of harder consistency which are useful for determiningthe topography of this region. In the posterior part there is athin and elongated plate, b, which passes from the lateral to the

1 The reasons for my using the terms 'dorsal' and 'regulator' nervesare given in the first part of my work. This Journal, vol. lxxv, 1932, p. 218.

THE INNEKVATION OF THE HEART OF CEUSTACEA 529

dorsal side. This plate is often well marked by a distinct pig-mentation. A second part of the tergite, a, which is of harderconsistency, lies in front of the plate h at the proximal end of theCoxale of the second Thoracopod (raptorial limb).

All the three regulator nerves lie superficially on the dorsalmuscles, and one ought to be careful when taking away thetergite as there is a danger of the nerves being torn awaywith it.

The following features concerning the situation of these nerveswhich we shall designate as nerves a, /?, and y are worthy ofnote! (Text-fig. 6).

The nerve a, taking an oblique course on the dorsal muscles,passes in front of the joint of the second Thoracopod.

The nerve fi crosses the medial margin of the muscles near tothe nerve a, but laterally the two nerves run at a greater distancefrom each other and the nerve /} passes behind the joint of thesecond Thoracopod.

The nerve y enters the heart at some distance from the nerve/?, but laterally the two nerves lie near to each other though theydo not unite into one bundle and the nerve y runs on the pos-terior margin of the plate b.

It is not difficult to see these nerves as they are representedin the figure, for they stain easily and in a short time. It issufficient to inject the dye under one of the abdominal tergites,and the dorsal nerves will appear deep blue sometimes alreadyafter thirty minutes. It is also possible to fix and mount prepara-tions in which these nerves travelling on the dorsal musclesremain in connexion with the heart. The Text-fig. 7 is drawnon the basis of such preparations. As we see in this figure bothnerves /? and y in their course on the thoracic muscles are incor-porated in the branches of the thoracic nerves Nn th in whichthey travel from the central nervous system. I did not succeed

1 I have chosen this designation by Greek letters instead of the moresimple by the numbers 1 to 3 as in my previous publication I had used theterm System I and II for designating two different sorts of fibres in thedorsal nerves. The homologues of these fibres are also present in theStomatopods. As these two sets of fibres are conveyed to the heart byt h r e e nerves a confusion would easily result if the nerves were alsoindicated by numbers.

Mm 2


in tracing exactly their proximal course, for the complicatedchitinous skeleton in this region makes the dissections verydifficult. It appears, however, evident that all the three regulator

ThIL

TEXT-FIG. 6.

Topography of the dorsal nerves of the heart. Ca, Carapace partlysectioned; Th II, second Thoracopod (raptorial limb); Co, Coxale;Siv, Sv, fourth and fifth body-segment; a, b, plates whichstrengthen the chitinous parts of the fourth segment; C, heart;a, /3, y, dorsal heart-nerves.

nerves spring from the large thoracic ganglionic mass. Thebranches which carry the nerves /? and y are most probably thenerves of the third and fourth Thoracomeres. As to the nerve ait belongs, of course, to one of the metameres situated anteriorly;but I am not able to state with any degree of certainty to whichof them it ought to be assigned. Probably this gap in myobservations could be filled up by the investigations of the larvalforms or of specimens with softer chitinous parts.

THE INNERVATION OF THE HEART OF CRUSTACEA 531

\ I

TEXT-FIG. 7.Junction of the dorsal nerves a, ft, and y with the ganglionic trunk

of the heart. Nn th, branches of the thoracic nerves carrying thenervesj8 and y; md, dorsal muscles; a, muscle-bundle with peculiarinnervation in which nerve-cells are also taking part (not men-tioned in the text). In the preparations from which this figure isdrawn, and which are mounted on slides, the heart is brought tothe same level as the dorsal thoracic muscles. The heart really liesdeeper than the surface of the muscles, and in consequence thedorsal nerves turn downwards to reach the heart.

In the preparations stained with methylene blue the threenerves in question have not the same appearance. The nerve a


is made up of one thick fibre only; arriving at the ganglionictrunk it divides into two branches of unequal calibre; onethinner runs forwards, the other thicker passes backwards.

The nerve /? does not present the same features in all thepreparations. Sometimes it looks as though consisting of onefibre only, in other preparations which are more completelystained this thicker fibre is accompanied by several thinner ones.The thicker fibre, on entering the ganglionic trunk, behaves inthe same way as the nerve a, i.e. it gives off a small branchrunning anteriorly while the main branch passes backwards.The thinner fibres are of unequal calibre and partly break up insmall granules. The nerve y has, like the former, one thickerand several thinner fibres (Text-fig. 8). The latter stain ingreater number than in the nerve /3.

The composition of the nerves /? and y of several fibres couldbe observed only in that part of their course where they are notincorporated in other nerves. On their way with the branchesof the thoracic nerves and in the ganglionic trunk these fibrescan be traced individually but for a very short distance.

In some preparations the thin fibres of the nerve y give offbranches before entering the ganglionic trunk (Text-fig. 8, a).These branches correspond perhaps to the nerves of the peri-cardial cavity described in Decapods. The thin fibres breakingup in small beads show sometimes structures resembling thosewhich stain so readily on the ligaments of the heart in Pa l i -n u r u s and S c y l l a r u s .

All the three dorsal nerves are enveloped by a pretty thicksheath probably of connective tissue. However, in my prepara-tions it does not stain with methylene blue and appears ratherhomogeneous.

2. E l e m e n t s of the dorsa l nerves in the gang l ion ict r u n k and t h e i r r e l a t i o n to the e l emen t s ofthe local s y s t e m .

There is no doubt that the elements of the dorsal nerves runthroughout the entire length of the ganglionic trunk. Thefibres of this origin are of various calibre, but even the stoutestdo not reach by far the size of the axons of the local neurons;


their staining in a deeper shade of blue and their somewhatdifferent outlines may also serve to recognize them among theelements of the ganglionic trunk, and help one to observe theircourse and connexions even in the posterior segments. On theother hand, however, as the tracing of each fibre separately

TEXT-FIG. 8.

Nerve y joining the ganglionic trunk Tr gang; a, fibres branchingfrom the nerve.

throughout many segments is practically almost impossible, theorigin of a given fibre from one or other of the dorsal nervescan only be suggested on the ground of some indications whichwe shall discuss later.

The aspect and the connexions of these fibres in the ganglionictrunk allow one to distinguish two sets of elements in themwhich are evidently homologues of those described by me in the

534 - J. S. ALEXANDROWICZ

Decapods as System I and II, and which I shall now call bythe same terms.

S y s t e m I.To System I can be referred the thicker fibres which enter

into relation with the nerve-cells, their collaterals, and theirdendrites. The diagrammatic Text-fig. 9 gives an idea of theseconnexions. The fibres, sv belonging to System I give offthin branches which have three fields of terminations. Some ofthem surround the cell of the local system, forming the basket-works already mentioned before, cf. fig. 6, PI. 31. They stainreadily, and are often deep blue when the cells are pale or evennot stained at all. The fibres assume a beaded shape and some-times expand to form leaf-like plates which are especially oftenstained on the most posterior cells. The fibres surrounding thecells pass also on to the main processes and interlace their'roots'.

From the fibres sx arise, further, thin branches, c, ramifying inthe trunk itself. They form fine networks of fibrils which aredenser in the anterior part of the trunk, though large compactmasses of the neuropile similar to those described in Decapodacould not be observed. This is evidently due to the elongationof the ganglionic trunk i n S q u i l l a . In the networks scatteredin the trunk the terminations of different fibres of System I meetwith one another as well as with the collaterals arising from thelong processes of the cells.

The fibres of System I give off, finally, thin branches, b, goingsideways from the trunk. They are nothing else than the'accessory fibres' described above as accompanying the rami-fications of the dendrites (fig. 10, PI. 31).

In the anterior part of the heart, especially between the fifthand sixth cell, I have often observed branches of System Iconsisting of several thin fibres which run sideways and ramifyon the muscles, apparently without connexion with the dendrites.As to their exact relations I am obliged to express the samedoubts as when describing them in the Decapods, namely, Icould not convince myself whether they are really independentof the ramifications of the dendrites or whether the latter aresimply not stained at this place.

THE INNEEVATION OF THE HEART OF CRUSTACEA 585

TEXT-FIG. 9.

Diagram showing the relation of fibres of System I, av to a neuronof the local system; col, collaterals; dd, dendrites; 6, fibres accom-panying the dendrites; c, fibres ending in fine networks in thetrunk.


Sys tem I I .System II consists of fibres thinner and more numerous

than the main elements of System I, but they stain rarely andindistinctly, in consequence of which it is practically impossibleto trace them at a greater distance. Travelling in the trunk thefibres in question branch successively sideways and run with thenerves of the local system. As shown in Text-fig. 10 one long

TEXT-FIG. 10.Fibres of System II, «2> accompanying the axons of the local system.

Stained by the method of Gross.

branch of the axon may be accompanied by several thin fibres,s2, of System II. Recalling what was said about the nervesarising from the ganglionic trunk, we come now to the conclusionthat long branches contain (a) one or more fibres given off bythe neurons of the local system, and (b) the fibres of System IIof the dorsal nerves. The latter are of much smaller calibre,and look as if they were only supplementary elements in thebranches of the trunk.

THE INNEBVATION OF THE HEART OF CRUSTACEA 537

Taking into account the above-mentioned difficulties ofanalysing the components of these branches, it might be objectedthat the thin fibres now considered as belonging to System IIare simply the finer fibres of other neurons which send smallerbranches to the nerves of the trunk. Of course, it is not easyto establish the criterion or distinguishing System II amongother elements. Some help has been afforded by the methodsof Cajal-Schultze and Bielschowsky-Gross since, after stainingwith silver salts, the fibres of System II become more deeplybrown than the others, and their presence in the ganglionictrunk and in the thicker nerves can then be recognized withgreater ease. Their small calibre may be considered as theircharacteristic morphological feature. Moreover, when tracingSystem II we do not notice the gradual decrease of the diameterof its fibres, whereas we notice it distinctly in the sub-divisionsof nerves of other origin.

The question of the endings of these fibres could not be satis-factorily solved. As the nerves of the local system which areaccompanied by the fibres of System II run to the muscles it isevident that the endings of System II are probably lying on themuscles too. Yet it is doubtful whether they always run inclose apposition to the fibres of the local system, or have theirown independent terminal branches. It is also a matter of doubtwhether fibres of System II exist which pass to the musclesdirectly from the trunk without joining the nerves of the localsystem. Although such conclusions might be drawn from somepreparations, I would still reserve my opinion upon this pointowing to the possibility of various errors.

If we summarize what was said above we can state that thesuggestion offered in our previous paper about the passing ofthe fibres of System II to the muscles has been strengthenedby the observations of the same elements in S q u i l l a , thoughprecise data concerning the distribution of the terminal branchesof this system cannot be given.

Turning now to the question of the origin of the two systemsof fibres I and II we can consider as certain that they are carriedto the heart by the three dorsal nerves a, /?, and y. But inwhich of these nerves run the fibres of each system ? Direct


observations, i.e. the tracing of fibres, are very difficult inS q u i 11 a since the elements of the main trunk are, especially inits anterior part, closely apposed to each other and, moreover,the staining of the individual fibres is, as a rule, not continuous,being often subjected to different interruptions. We have there-fore to arrive at some conclusion in an indirect way.

It is to be remembered that the nerve a consists of one thickfibre only, whereas the nerves /J and y are each made up of onethick fibre and several thinner ones. The thick fibres of all threenerves, so far as they could be traced in the trunk, behave inthe same way. They send off branches which seemingly enterinto close relations with each other just as do the fibres ofSystem I in the Decapoda. Taking into account that, in theDecapoda, System I is composed of three thicker fibres on eachside, it seems admissible that the same number of elementsbuild up System I in Stomatopods. In consequence this systemin S q u i 11 a would be made up of six fibres conveyed to theheart by all three paired dorsal nerves. In the ganglionic trunk,however, especially in its middle and hinder parts, these fibresdo not stain in the same preparations all at once, and we findmostly two of them in one preparation.

As to the elements of System II they are given off, accordingto all probability, by the thinner fibres of the nerves fl and y.

According to this interpretation the nerve a carries fibresonly of System I, whereas the nerves /? and y contain elements ofboth Systems I and II.

I tried to get more convincing evidence by investigating theeffects of stimulation of the regulator nerves. To the excitationof the nerves /} and y by means of induced currents the heartresponds with an acceleration of its rhythm. By the excitationof the nerves a the slowing of the heart has been obtained, butonly in some experiments, while in others the stimulation wasnot effective. It may be that in the last case the excitabilityof the inhibitory nerves had been abolished in a very short time.

These experiments allow two interpretations. One may admitthat the nerve a carries the inhibitory impulses while nervesj8 and y are accelerator nerves. But the explanation is alsoadmissible that the nerve a is an inhibitory nerve whereas /?


and y contain both kinds of fibres, i.e. the inhibitory and theaccelerator ones, but that the action of the latter is predomi-nating when the nerves are excited by means of the electricalcurrent.

At any rate the fact that the nerve a which is made up of athick fibre slows the rhythm of the heart, lends support to thesuggestion that System I in the heart of the Crustacea has thesame function as the vagus in the Vertebrate animals.

V. NERVES OF THE ARTERIAL VALVES.

As was emphasized in the general description of the nervesin the heart, the system of the valves consists of (a) the seg-mental nerves of the heart, and (b) the anterior cardiac nerve.

1. N e r v i s e g m e n t a l e s co rd i s 1 (Text-figs. 1 B, 11,and 12B)The segmental nerves originate in the ganglionic chain of the

central nervous system, and in their proximal course are in-corporated in the thoracic and abdominal nerves. Travellingwith those branches of these nerves which pass on the dorsalside of the flexor muscles they leave here the somatic nervesand, independent of other elements, proceed to the heart. Asthey stain a deep blue colour it is possible to recognize them evenin the somatic nerves, but I was unable to follow them separatelyup to the ganglionic cord. It is probable that in the centralnervous system the neurons to which these nerves belong arein some relation with each other, but in their peripheral coursethe nerves of one segment have no connexion with those of thenext segments. Only the valve of the last pair (XV) of the arterieshas a common innervation with the valve of the posterior aorta.The independence of the nerves of each pair of valves, a featurein which the Stomatopods differ from the Decapods, is notdifficult to ascertain owing to the distance of the valves from

1 This nomenclature might be found inappropriate since a part of thesenerves do not correspond to the body-segments but to the metamericarrangement of the nervous elements. As was noted before the fourth body-segment is made up of the first four and a part of the fifth Thoracomeres.Nevertheless I have left this term 'segmental nerves', already used whendescribing homologous elements in Insects and in the Decapod Crustacea.

540 J. S. ALBXANDROWICZ

each other and the distinct staining of the nerves in the majorityof them. However, the nerves in the four anterior arteries stainrarely and incompletely, and therefore, though their arrange-ment seems to be the same as in the other valves, I cannotconsider it as established by strong evidence.

As the Text-fig. 11 shows, each segmental nerve, N seg, con-

TEXT-FIG. 11.

Innervation of the valves of lateral arteries. C, heart-tube viewedfrom the ventral side; N seg, segmental nerves of the heart; a, leaf-like plates.

sists of a small quantity of fibres which give off characteristicbranches dividing among the muscles of the valve. Beforedoing so each segmental nerve sends an anastomotic fibre tothe contralateral nerve, and through it takes part in the nerve-supply of the opposite valve.

The arrangement of the nerves in the last pair of valves isrepresented in the Text-fig. 1 2 B. The nerves approach theheart running alongside the posterior aorta, ao p, where they giveoff anastomosing fibres and finally send off branches to themedian and the two lateral valves. The course of the nervesrunning on the posterior aorta up to their origin could not be

THE INNBEVATION OF THE HEAKT OF CRUSTACEA 541

traced out. I think that they are nothing else than the last pairof segmental heart-nerves.

The branching and the endings of the fibres in the valveshave the same appearance as in the Decapods. The thinnerbranches ramifying among the muscle-fibres of the valvepresent many varicosities or even are split into small granules.Larger leaf-like plates, a (Text-fig. 11), are also frequentlypresent; they are mostly situated on the branches directedtowards the surface of the valve. Whether or not they areartificial structures I cannot state decisively.

2. N e r v u s c a r d i a c u s a n t e r i o r (Text-figs. 1 B and 12 A).

The anterior heart-nerve runs alongside the anterior medianartery to end in its valve. The situation and the ending of thisnerve are therefore the same as those of the nerve of Lemoinein the Decapods. In the latter animals the cardiac nerve hasbeen described as belonging to the so-called stomatogastricsystem. In the Stomatopods the same system was investigatedby Police in 1909, but the point of origin of the heart-nerve wasnot indicated by this writer. Further observations are necessaryto elucidate this question as in my preparations the anteriorcourse of this nerve is not sufficiently stained. Its endings arerepresented in the" Text-fig. 1 2 A, in which we see that theanterior nerve, in the vicinity of the heart, divides into twobranches which ramify when penetrating the anterior medianvalve. The terminal fibres on the muscles are of much the sameappearance as in the remaining valves. No, connexion has beenobserved between the branches of the anterior cardiac nerve andthose of the segmental nerves.

From the above description it results that so far as can bestated, the segmental nerves and the anterior heart-nerve donot give off branches to the wall of the vessels, but are destinedfor the innervation of the valves only.

Nusbaum (1899) claimed to have observed nerve-fibres andnerve-cells on the ventral subneural vessel of S q u i 11 a. I didnot see these elements.


DISCUSSION.

I shall now endeavour to consider from the physiological pointof view some points of the results described above.

With regard to the neurons of the local system, the assumption

TEXT-FIG. 12.

A, Innervation of the valve of the anterior aorta. N card ant,Nervus cardiacus anterior. B, Innervation of the valves of theposterior aorta, aop, and of the fifteenth pair of arteries.

that the long branches are motor elements is the most probableof all. These branches, therefore, convey the impulses from thecells to the muscle-fibres. As to the short arborescent projections,


I consider them as dendrites which carry impulses from theperiphery of their ramifications to the cells or to the axons.1

The fact that the endings of the dendrites are doubtless situatedon the muscle-fibres has induced me to think that the contractionof the muscles acts as stimulus on the receptor parts of theneurons, and in the previous paper I have assumed that in thisway a self-regulation of the neuro-muscular apparatus of theheart can be realized. Taking now into account the arrangementof the nervous elements in S q u i 11 a, it seems worth while tosuggest that the excitation of the dendrites of a given neuron,caused by the contraction of the muscle-fibres, is propagatedalong the axon and its branches and on discharge causes acontraction of other muscle-fibres.

The course of the impulses according to our hypothesis isrepresented in the diagram Text-fig. 1 3 A. Suppose an impulseconveyed by the axon, a, starting from an element whose celllies in one of the farther segments, causes contraction of themuscle-fibres mv This state of the muscles stimulates thedendrites of the cell b, and the resulting impulse is propagatedthrough the axon to the muscles ra2 which contracting in theirturn stimulate the dendrites of another cell, c. It is conceivablethat by an appropriate distribution of the fibres the dischargeof an impulse in any one of the neurons can involve the co-operation of the whole. In organs where the nerve-cells lie nearto each other, their situation facilitates various interconnexions.In the long heart-tube of the Stomatopods, however, there mustexist a special distribution of the nerve-elements, but I was ableto decipher only a few features of this arrangement. As such,maybe recalled here the behaviour of the axons,which in varioussegments most probably take the different course and, further,the fact that several axons send off their terminal branches tothe same segment. Moreover, the situation of the dendrites ofone cell is of such a kind that one may admit that the receptoryarea of each neuron embraces the muscle-fibres in a part of the

1 We are compelled to add the words 'or to the axons' since a part ofthe dendrites arise from the axons and we cannot know whether theimpulses conveyed by these dendrites pass through the nucleated cell-bodies or go directly to the branches of the axons.

NO. 304 N n


TEXT-FIG. 13.

Diagrams showing the hypothetical course of impulses in the localsystem of the heart of Squi l l a m a n t i s . The interruptions ofthe axons in the drawings show that these processes are long anddo not end in the segments next to those in which lie the cells.

THE INNBRVATION OF THE HEART OF CRUSTACEA 545

heart approximately equal to the length of one segment. Thearea of the motor-fibres of the same neuron does not lie in thesame segment as the receptory area and seems to be larger, sothat one neuron innervates the muscles of more than onesegment. With respect to our hypothesis the observed factswould indicate: firstly, that one nerve-cell can receive impulsesfrom different neurons since the muscles in which end theirdendrites can be caused to contract in response to stimuli comingfrom more than one neuron; and, secondly, that one excitedneuron can transmit the impulses to several others. Accordingto this interpretation our second diagram, B, shows the neuron breceiving stimuli from the neurons a, d, and e, and the neuron aending in the muscles mx and m2, and in this way transmittingimpulses to the cells of different segments.

If our suggestion would hold good for other organs endowedwith autonomy of movement, we might conceive that in depen-dence on the arrangement of the nerve-elements, on the velocityof the propagation of the impulses, and on the quickness of thereactions which are taking place, the co-operation of thedifferent parts of the organ can be either almost simultaneousor in other organs the contraction of the muscle-fibres can occur,as e.g. in peristalsis, in a definite succession.

The connexions of the neurons in the heart of S q u i l l aappear still more complex if we take into account the networksgiven off by the collaterals. It is doubtful whether these neuropilesmerely serve as fields of conjunction between the local systemand System I of the dorsal nerves, or whether they bringalso into relation the neurons of the local system with each other.

As regards the system of the e f fe ren t n e r v e s which areacting as regulator fibres of the beat of the heart, we have alreadysuggested that the thicker of them, termed System I, have aninhibitory function. They are in relation with the cell-bodies,their collaterals, and dendrites. Even admitting that somefibres of System I have another destination, the histologicalevidence seems to prove that the ' vagus system' of the heart inthe Crustacea acts on the local neurons—on their cells and ontheir short projections.

This evidently does not apply to the second kind of regulator

546 J. S. ALEXANDKOWICZ

fibres, System II, which as we suppose conveys the accelera-tor fibres. They are provided with long branches of the localsystem ending on the muscles. As regards their action two wayscan be imagined: these fibres convey the impulses either tothe motor endings of the local system, or directly to the muscles.We should have to arrive at the latter conclusion were it provedthat the accelerator fibres end on the muscles independentlyof the other nerves. There are some reasons for believing it,but strong evidence as to the exact course and connexions ofthese fibres cannot be brought forward.

The nerves of the valves are remarkable for their independencein the different segments in Squ i l l a , whereas in the Decapodsmerely the nerve of the anterior aorta is unconnected with thoseof the remaining valves. The arrangement of these nerves inStomatopods reinforces the supposition expressed by me in myprevious publication, that the function of these nerve-elementsconsists in the maintaining of the tonic contraction of themuscles of the valves. One must conclude that in systole somefactor must enter into action provoking the relaxation of themuscles and permitting the outflow of the blood into the arteries.

SUMMARY.

1. The t h r e e sy s t ems of n e r v e s , viz. the local system,the regulator nerves, and the nerves of the arterial valves, whichwere previously described by the writer as innervating the heartof the Decapod Crustacea, have also been found in Squ i l l am a n t i s .

2. The local sy s t em consists of not less than fourteenneurons. Their cells are situated in a nerve-trunk runningalongside the dorsal surface of the heart, and, with the exceptionof the three anterior elements, lie at regular intervals eachbehind a pair of the ostial orifices. The cells give off the followingprocesses: (a) the axons which form the chief part of the fibresin the ganglionic trunk and which after sending off many branchesend on the muscle-fibres of the myocardium; (&) the dendrites—short arborescent branches arising both from cell-bodies andaxons, and ending in the neighbourhood of the trunk on the


muscle-fibres too; (c) short collaterals ending in fine networksof fibrils in the ganglionic trunk.

3. The system of r e g u l a t o r n e r v e s connecting the localsystem with the central nervous system, in the Decapoda con-sisting of one pair of nerves, is represented in the Stomatopodaby three paired nerves which in our description have beentermed N e r v i c a r d i a c i d o r s a l e s . For the designation ofeach of them the letters a, /S, and y have been used. Their courseindicates that they originate in the large thoracic ganglionicmass. After passing on the dorsal side of the extensor musclesthese nerves approach the heart from its dorsal side, and enterits ganglionic trunk in the region of the fourth body-segment.The nerve a is made up of one thick fibre only, the nerves /3and y contain one thick and several thinner fibres each.

In the ganglionic trunk two sets of fibres given off by thedorsal nerves can be distinguished: one of them, termed SystemI, is made up of thicker fibres whose branches give synapseswith the cells, collaterals, and dendrites of the local neurons; theother, called System II, consists of thinner fibres accompanyingthe long branches of the axons which pass to the muscles.

4. The system of n e r v e s s u p p l y i n g t h e ' a r t e r i a lv a l v e s is made up of (a) the anterior cardiac nerve running tothe valve of the anterior aorta; and (b) the segmental nervesof the heart passing in each metamere to the valves of the pairedarteries. There are, in all, fifteen pairs of these nerves. The lastpair supplies the valves of the fifteenth pair of arteries and thevalve of the posterior aorta. Each segmental nerve sends offanastomotic branches to the contralateral nerve, but does notshow any connexions with the nerves of the neighbouring seg-ments. In this respect these nerves in S q u i l l a differ fromthose in the Decapods since in the latter they are all intercon-nected by anastomosing fibres. On the other hand, in S q u i l l aas well as in Decapods the anterior cardiac nerve has no con-nexion with the segmental nerves of the heart.

5. With regard to the function of the nerve-elements enumer-ated above, the local system is to be considered as an autonomicapparatus which rules the beat of the heart, whereas the dorsalnerves convey the inhibitory and accelerator impulses from the


central nervous system. The first of the dorsal nerves, a, has beenfound carrying the inhibitory impulses. The stimulation of thetwo following nerves, /? and y, quickens the beat of the heart,but this effect of the physiological experiment does not excludethe possibility that the nerves /? and y contain both inhibitoryand accelerator fibres.

The two sets of fibres in the ganglionic trunk which have beentermed Systems I and II are probably concerned the former withthe inhibitory and the latter with the accelerator action.

The function of the nerves of the arterial valves probablyconsists in the maintaining of a tonic contraction of the musclesof the valves.

LITERATURE CITED.Claus, C. (1883).—"Die Kreislauforgane und Blutbewegung der Stomato-

poden", cArb. Zool. Inst. Wien', v.Giesbrecht, W. (1910).—"Stomatopoden." I. Teil, 'Fauna und Flora,

Neapel, Monogr.' 33.(1913).—"Crustacea." 'Handb. der Morphologie der wirbellosen

Tiere v. A. Lang.'Milne-Edwards, M. (1834).—'Histoire naturelle des Crustaces', tome i.Nusbaum, J. (1899).—"Beitr. zur Kenntnis der Innervation des Gefiiss-

systems ... . b. d. Crustaceen", 'Biol. Centr.', xix.(1899).—'Materyaty do anatomii i histologii obwodowego ukladu

nerwowego skorupiakow.' Kosmos.Police, G. (1909).—"Sul sistema nervoso viscerale della Squilla mantis",

'Mitt. Zool. Station NeapeF, xix.

EXPLANATION OF PLATE 31.

Figs. 1-7.—Ganglion cells of the heart of Squi l la m a n t i s , l a , ft,2, 3, the first, second, fifth, and eighth cell drawn from the same prepara-tion; 3 d, dendrite arising by means of three trunks; 4, cell with three pro-cesses; col, collaterals; 5, cell with four processes; 6, the fourteenth cell withthe pericellular network arising from fibres sx of the dorsal nerves; 7,ganglion cell with the proximal parts of its main processes made up ofseveral fibres. The number of these roots is in reality greater than repre-sented in the figure, a, branches arising from the roots; b, cleavage of theprocess.

Fig. 8.—Endings of a dendrite in two layers of muscle-fibres, ms, super-ficial muscle-bundles.

Fig. 9.—Endings of a dendrite in the muscles.Fig. 10.—Accessory fibres which accompany the ramifications of a

dendrite.Fig. 11.—Nerve-cell with its dendrites.

J. S. Alexandrowics, del.

Quart. Journ. Micr. Sci. Vol. 76, N. 8., PL 31

rlmm

1-0

the innervatio onf th heare t of crustacea . ii. stomatopoda.precisely 8-5 cm. thirty-two arteries...

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