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It is observable, however, that the presence of vibratilecilia in the first embryonic form is a character of littleimportance, and cannot serve as the basis of a naturalclassification.

REMARKS on OPALINA and its CONTRACTILE VESICLES, onPACHYBEKHON and ANNELIDAN SPSKJIATOPHORS. ByE. RXY LANKESTER, B.A. Oxon. Plate IX.

IN examining the anatomy of oligocheetous Annelids, Ihave necessarily met with certain species of Opalina, thatcurious mouthless genus of Infusoria the life history ofwhich, like that of so many of the class, is as yet quite un-known. Some notes on the Opalina Naidos of Dujardin,which abundantly infests the Nais serpentina, may not beuninteresting1; at the same time, I offer some evidence as tothe nature of the bodies which Professor Claparede consideredto be Opalinoid parasites, and termed Pachydermon, figuringthem from two species of the oligochset Clitellio; butwhich I think, from the characters of some observed by mein another worm (namely, Limnodrilus) must be consideredas packets of spermatozoa or suermatophors.

OPALINE.—The genus Opalina has sometimes been madeto include those pyriform ciliated animalcules which swarmin the rectum of the common tadpole and in similar situations,called Bursaria Ranee by Ehrenberg ; but these forms shouldrightly be separated from those so frequently found in bothmarine and freshwater Annelids, from which they differmaterially, as pointed out by Claparede in his work withLachmann on the Infusoria.

The simple structureless body of these first-named para-sites has really very little in common with Opalina, properlyso called—an abundance of highly refrangent granules beingthe only differentiated portions of its substance (PI. IX, fig.9), no trace of the nucleus and contracted vesicles, nor ofthe furrowed cuticle of true Opalina being observable. It isnot improbable that these swarming ciliated flakes of sar-code—for they are nothing more—may undergo subsequentmetamorphosis of the most extreme character ; but what istrue of them.does not apply to veritable Opalina.

Opalinse of the type I am aboiit to describe have beenobserved by Dujardin, Schultze, Schmidt, Stein, and Clapa-rede in various worms. Thus we have Opalina Naidos,

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Dujardin, in Nais ; 0. polymorpha, Schultze, in Planariatorva j 0. lineata, Schultze, in Nais (?) littoralis ; O. recurva,Claparede, in Planaria limacina; 0. prolifera, Claparede,1

in a supposed marine Nais; 0. filum, Claparede, in Clitellioarenariusj 0. ovata, Clap., in Phyllodoce; O.convexa,C\a,p.,in another Phyllodoce ; 0. Pachydrili, Clap., in Pachydrilusverrucosus; O. uncinata, Schultze, in Planaria ulvce ; 0.armata and 0. falcifera, Stein, in Lumbricus terrestris andL. anatomicus—these three species bearing hooks are placedin the genus Hoplitophrya, Stein; whilst another species,formerly known as Leucophrys stiata, is called Anoplophryalumbrici. At the same time, Hoplitophrya armata is sup-posed by Stein to be a later development of A. lumbrici.

Though they are common enough there appears to havebeen doubt as to the character of Opalinse; first as to thenature of the yesicles which they possess, and secondly, asto the nucleus. Schultze described a series of contractilevesicles in his O. lineata; and Claparede subsequently sawvesicles in another Opalina, but could not succeed in wit-nessing their contraction. In the species which he has mostlately described, however (" Recherches sur les Annelides,Turbellaries, &c, observes dans les Hebrides"), he statesthat he has observed the contraction of the vesicles.

In certain species found in Planarise a single long con-tractile vesicle has been said by Schultze to exist, taking theplace of the series of smaller vesicles. A nucleus of varioussize and distinctness has been described in these true Opalinte,but never a nucleolus. Stein describes the nucleus of 0.armata^ as presenting oval embedded granules and rod-likebodies.

The two forms occurring in the Earthworm (0. armataand O. fulcifera), as well as 0. uncinata, from a Planarian,possess a pair of recurved hooklets, which, situated at oneend, are believed to furnish a means of attachment, as insome Gregarinse (G. Sieboldii, K.61L, from Libellula larva).The tooth-like body of Dysteria (Huxley, ' Quart. Journ.Microsc. Sci.,' Vol. 5, 1857, p. 138) furnishes a paralleldevelopment in an adult ciliate Infusorian.

From the general statements with regard to Opalina, ex-cluding from consideration the so-called Bursaria Rants andsimilar species, there seems to be no reason for supposingthat they are anything but Infusoria; the supposition thatthey are a phase in the development of certain .worms being

1 This species is peculiarly interesting, since it is distinctly a segmentedanimal—as much as anj Tcenia—presenting a cbain of incomplete zooidsattached one behind the other.

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curiously inconsistent with the existence of the nucleus, thecontractile vesicles, and the ribbed ciliated cuticle of a typicalInfusorian.

In PI. IX, fig. 1, is drawn a fair average specimen of theOpalina infesting Nais serpentina, It is about the 1-200thof an inch long, flattened very considerably (so as to bebaawl-Kke),. and of an oblong form. Hundreds are oftencrowded together in the intestines of the Nais; and sotightly packed are they that frequently some specimensgrow into an irregular shape, as seen in fig. 8. They do notvary much in size in the same worm; but in Lumbriculvs Ihave seen what I believe to be the same species, as largeas one fiftieth of an inch, and with thirty contractilevesicles.

Many of the specimens brought out on to the field of themicroscope, by causing the worms to burst, are seen to be inthe act of transverse fission (fig. 7) ; and their increase insize appears to be prevented by this removal of a portion ofthe individual. Those that have been recently separated bytransverse fission have a pointed anterior extremity, which gra-dually assumes a flat and blunted character as growth proceeds.Usually when a Nais is placed on a glass slip, and squeezedbeneath the thin cover, so as to cause the Opalina to beextruded, it is noticed that, though at first they move rapidlyabout the field of the microscope with a regular and activemovement of their long cilia, yet slowly and surely thesemovements become weaker and intermittent—the cilia alto-gether ceasing and then resuming their action ; until at lastmovement ceases altogether. When first extruded theobserver will have noticed the great transparency of theOpalina, and will scarcely have been able to define the largenucleus (fig. 1, n) indicated by a somewhat darker tint; buthe will have caught sight of the row of globular spacesusually confined to one side of the body, and will probablyhave watched in vain for their contraction.

Now, when the ciliary motiou has ceased, it will be seenthat some of the globular spaces have acquired a great size(fig. 2); whilst the nucleus has become very distinct, beingdefined by a broad space running round it, and having thesame pink or purplish tint which is so characteristic of thecontractile vesicles of all Infusoria. The death of the Opalinahas been caused by its sudden introduction to fresh water—the distension of its contractile spaces, and the formation ofthe cavity between the nucleus and peripheral tissue beingequally caused by the rapid endosmose of water. It seems veryprobable that this action of pure water upon an organism

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adapted to live in intestinal fluids accounts for the difficulty"which many have experienced in witnessing the contractionsof the contractile spaces in Opalintz. It also accounts for theoblong vessel surrounding the nucleus in some of the speciesfigured by Stein, as it most certainly produces this appearancein the Opalina which I have studied.; and it also explains thenucleus-membrane as distinct from nucleus-content of whichStein speaks.

The long vessel of Opalina Planaria described by Schultzemay possibly be also due to such a separation of the innerand outer layers of the organism by the imbibition of water,since in my Opalinse the cavity so produced had most closelythe appearance of a long vessel, for which I mistook it atfirst. In the Opalina of Olitellio I observed and drew a longvessel, produced, I now believe, in this way. The im-bibition of water, besides distending some of the vesicles,may cause them to run together, and form much largerlacunje than ever exist in the living animal, as in fig. 2, y.

To avert the death and rapid post-mortem changes of the0palina3, it is only necessary to avoid using water and letthe parasites, when extruded, remain in some of the fluidsfrom the worm. If arranged in this way they will be seenas in fig. 1; and the rapid contractions of the series ofglobular cavities arranged on one side of the creatures maybe watched when once the eye has got accustomed to theirmovements, and very few more beautiful sights can be pre-sented to the observer.

As the Opalina rolls slowly over on to one side, theattention may be fixed on one of the globular cavities, whichappears like a small pink bladder floating in the perfectlycolourless sarcode of the Infusorian. Suddenly as you watchthis bladder—so suddenly that you are almost startled—thebladder is gone ; but almost immediately in its place a veryminute spot is seen, which slowly increases in size, and ulti-mately proves to be the same cavity reappearing.

Dr. Moxon having recently, in the ' Journal of Anatomy '(May, 1869), written on the subject of the contractile vesicleof Infusoria, advancing arguments in favour of the view thatit opens externally, I may here point out certain appear-ances which are visible in Opalina, and which seem clearlyto accord with this view; though, at the same time, I shouldsay that there can be no doubt about the opening of thevesicle, after the paper of Dr. Zenke, noticed in this Journaltwo years since. In fig. 2, in which the vesicles are dis-tended by an excessive endosmose, they are seen to have alemon shape, more or less, the point being nearest the

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cuticle. This is exactly the form presented by the vesicles(or rather cavities, for they have no proper memhrane) justbefore disappearing in the living Opalina, if seen in profile,and seems to favour the idea of their opening externally.When the cavity is reappearing, after collapse, it has aglobular form from the very first, increasing gradually at itsperiphery, but maintaining its globular form, as seen in fig.6j a, b, c, d, e, until the full dimensions are attained. Onsome occasions during the collapse I have observed that thistakes place in a totally different way, the opposite M'allsclosing together, as in / , g, h. This mode of expansion andcontraction clearly agrees with the supposition that thesepulsating cavities are yielding points in the sarcode substance,which are slowly distended by the accumulation of fluid;the thin external wall ultimately bursting and allowing thefluid to escape; and then the]adjacent parts unite again at onceas sarcodic matter is known to do, and a fresh accumulationcommences at the old place. The formation of elongated cavitiessurrounding the nucleus, and having all the appearance ofthe regular " vesicles," as well as the. fusion of adjacentcavities, and the continued distension of others after death,by the excessive endosmose of liquid, all seem to favour thesame theory of the formation and mode of action of thecontractile cavities.

The cavities vary much in number in the Opalinje Istudied; very rarely they occurred on both sides of the body,but were generally in a series of from five to ten on one sideonly. Those in immediate proximity to one another appearedto contract in succession, but there were sometimes two orthree points of departure, as it were. Frequently a gapoccurs in a series, which evidently ought to be filled up bythe reappearance of a collapsed cavity; but after longwatching it does not reappear. The time of contraction andexpansion of the same cavity varies, but the collapse occursa little less frequently in active Opalinae than twice a minute;thus one cavity or other is almost constantly contracting.

So much with regard to the " cavities." The substancein which these cavities are placed is almost homogene'ous andcolourless, but in the living Opalina a layer of fine highlyrefracting granules is seen to underlie this (ff), and some ofthe fine granules are scattered in the cortical substance. Thelayer of granules marks out and bounds the great nucleus n,which in the living creature is not very different in appear-ance from the rest of the structure. A very slight additionof acidulated water, however, brings out the nucleus verydistinctly, as in fig. 3. It is also rendered very obvious if

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the Opalina is allowed to die in water, a cavity forming thenbetween it and the layer of granules belonging to the deeperpart of the cortical substance; which, as remarked above,might be mistaken for a normal structure, and I think hasbeen by Schultze and Stein in other species. With a goodone eighth a very definite structure is revealed in the nucleusafter treatment with dilute acetic acid. Minute round nucleiare embedded in its substance exactly as has been so oftenfigured and described in the nucleus of many Infusoria. Inthe face of this structure it is difficult to understand how theOpalinee can be refused a place among Infusoria proper, orsupposed to be stages in the development of worms.

The cuticle is sharply ridged in this species of Opalina,as in other true Opalinse, which is not the case in the so-called Bursaria Ranee.

The Opalina infesting Clitellio arenarius is not unlikethe one from Nais serpentina, but it is much longer. I haveobserved that from Clitellio in the Isle of Man. Claparedehas found it also, and termed it Opalina filum. The anteriorextremity presents -a broad emarginate area, which is notseen in O. Naidos, nor in the very long specimens of 0. Naidoswhich I once found in Lumbriculus at Hampstead.

Perhaps the most interesting form of Opalina is that namedO. prolifera by Claparede, observed by him in a small oligo-chset. This form was seen by him reproducing by transversefission, but in such a way that several partially separated budsremained attached in a chain. In fact, we have here achain of imperfect zooids, forming a segmented organism,exactly as a segmented wnrm is formed.

PACHYDERMON.—In fig. 10 is drawn a structure which Ifound in the spermatic reservoirs of a new species of Limno-drilus, a genus of Oligochsets allied to Tubifex, and establishedby Professor Claparede. I found three of these curiousstructures in each reservoir of a Limnodrilus which hadrecently undergone copulation, as was indicated by the con-dition of its copulatory organs; whilst in those which hadnot copulated I never found them.

If this is a distinct parasitic organism it evidently belongsto the genus Pachydermon of M. Claparede, two species ofwhich he has described in his ' Hecherches sur les Oligo-chetes,' from two specimens of the genus Clitellio (Oligo-chseta). It is also clearly identical with the appearancefigured and described by the late M. Jules d'Udekem fromthe spermatic reservoirs of Tubifex; but I most assuredlycannot regard any one of these structures as indicating anOpalinoid, as does M. Claparede, for whose opinion I would,

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however, express the very greatest respect. There is no tracein those I obtained from the Limnodrilus of any distinct cuticle,of any contractile vesicle, nor of a nucleus-like structure ;neither does the dense hair-like fringe exhibit any movementlike that of cilia, though I watched the supposed organismwhen within the spermatic sac. M. Claparede observed languidciliary movements when, the Pachydermon was placed insalt water, which is not what we should expect in the caseof an Opalina. On the contrary, I think these remarkablestructures must be regarded as spermatophors—aggregationsof spermatozoa, perhaps cemented and worked into this shapethrough the secretion and action of the spermatic sac. Thedotted appearance of the central portion of the spermatophoris caused by the aggregated heads of the individual sperma-tozoa ; whilst the dense fringe is due to their pendant andinterwoven filaments. As indicated in the drawing, thefilaments do not all stand out in one direction from the morecentral portion of the mass, but are crossed and interwoven,a circumstance which is not indicated in M. Claparede'sfigures of Pachydermon.

If one of these masses be broken by pressure, very con-clusive evidence is obtained that we have not to do with anInfusorianf but that the mass is composed of aggregatedfilaments such as spermatozoa. No cuticle is ruptured bythe pressure, and no differentiation of the supposed sarcodicmaterial is disclosed, but simply a felted structure, composedof innumerable filaments. In fact, everything that I wasable to ascertain with regard to these bodies tended toshow that they were simply masses of spermatozoa woventogether and agglutinated in that very remarkable mannerin which we know spermatophors are produced in othercases. Spermatophors have been described in the Polychaota(by M. Claparede himself), and hence we may fairly ex-pect them in the Oligochseta.

M. Jules d'TJdekem regarded the bodies which he observedas connected with the formation of the egg-capsule, havingmistaken the spermatic reservoirs for an egg-capsule secretinggland. Similarly he described long filaments in the sper-matic reservoirs of Stylaria, as destined to strengthen theegg-capsule of that Naid.

In the spring (of 1869) I made some careful studies of thegenital organs of Nais serpentina; and in the enormousspermatic reservoirs which develop in that Annelid at a lateperiod of its sexual history, I found long coiling filaments,having a fibrous structure (figs. 11, IS). These, no doubt,are identical with the filaments seen by d'Udekem in Stylaria,

VOL. IX.—NEW SER. L

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and I am inclined to consider them also as spermatophors;identical thus in their nature with the Pachydermon ofClaparede. In the spermatic reservoirs of Nais serpenlinawere also a few floating spermatozoa and very remarkahleflat ihombic crystals of small size, which disappeared on theaddition of weak acetic acid. If this interpretation of Pachy-dermon and of the coiling filaments, of the spermatic reser-voirs of Nais be correct, we may state, as a new and notunimportant fact, that spermatophors are developed in thefollowing genera of oligocheeta, viz. Clitettio, Tubifex, Limno-drilus, Nais, and Stylaria.

KEFEKENCBS. Opalmce.Schultze.—Beitrage zur Naturgesch. der Turbellarien.

Greifswald, 1851.Stein.—Die Infusions thiere auf ihreEntwickelungsges-

cbicbte untersuckt. Leipzig, 1854. P. 181.Stein.—Der Organismus der Infusions tbiere. lste

Abtheilung, 1 vol. folio. Leipzig, 1859. P. 91.Claparede et Lachmann.—Recherckes sur les Infusoires.

Geneva.Claparede.—Recherches sur les Annelidas, Turbellarie's, &o.

Observ6s dans les Hebrides. Geneva, 1860.

Pachydermon.Claparede.—Recberches sur les Annelides, Turbellarie's, &c.

P. 88, PI. IV, fig. 1 and la.Claparede.—Recberches Anatomiques sur les Oligocbe'tes.

Geneva, 1862. Plate IV, fig. 12.D'Udekem.—Hist. Nat. du Tubifex rivulorum. Mem. de

l'Acad. de Belg. Tom. 26. 1S55.D'Udekem.—(As to Stylaria). D6veloppement du Lombric

terrestre. Mem. de l'Acad. de Belg. Tom.27. 1S56.

Claparede and Mecznikow.—(Spermatophor of Spio). Beitrage zur Eentnissder Entwiok. der CliEetopoden. Zeitschr.fur wiss. Zoologie. Bd. XIX.

On MICROSCOPIC ILLUMINATION. By JOHN F. HIGGINS,A.M., M.D. Eead before the American MicroscopicalSociety of the City of New York, October 12th, 1869.

T H E subject of illumination in the use of the microscopeis one upon which much has been written, especially in con-nection with the merits of various accessories, and yet onethe understanding of which is far from general, and, more-over, in reference to which microscopists of acknowledged