aristotel driesch

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I nt . .J . Dev .l Ji ol . ~O : 21 -26 ( 1996 ) 21

From the Aristotelian soul to genetic and epigeneticinformation: the evolution of the modern concepts in

developmental biology at the turn of the century

Creature made by the hands ot God. animated image of theEternal, or mere product of a soulless nature, just a physico-chem ical system - what is man, what are living beings? Thesequestions im plicitly w ere driving forces w hen the occidental urgefor knowledge turned to the rnystery of developrnent. The changefro m re lig io us p re co nc ep tio ns a nd p hilo so ph ic al c on sid era tio nsto modern scientific concepts took place around the turn of thecentury a nd culmi na te d in the recognition of internal (genetic)information as a n essentia l princip le governing livin g beings.Are living beings m achines?

When the educated laity of the 17th and 18th centuries.devoted to rationalism, began to abandon the hitherto prevailingChristian-Scholastic philosophy and creed, the animate beingsof the living world w e r e more and more transformed into self-motive machines comparable to the admirable astronom icclocks being built by the contemporary artisans. This turn in theview of living beings was prepared by philosophers such asDescartes and Leibniz, and catalyzed by a spiritual uprisingwhich brought forth the modern natural sciences. W hen inphysics new branches such as the study of electricity, optics andtherm odynam ics cam e into bloom , the term mechanical adoptedmore and more the meaning of physical, and the term physical,supplemented by the appendix chemical, becarne almost syn-onym ous w ith natural.

As Klaus Sander (1991 a) in his essays "Landrnarks inDevelopmental B iology" pointed out, the term "Mechanik" in"Wilh elm Rau x's A rc hiv fU r Entw ic ke lu ng sme ch an ik " sta nds for'natural causation'. Nevertheless, much thinking in terms ofmechanical engineers and artisans was left. Thus, August

W ER NE R A . M ULLE R*Zoolog isches Inst itu t, Ruprech t-Karfs-Univers ita t, He ide lberg,Germanv

Weism ann (1892) envisioned a cornplicated m achine that splitsup the hereditary substance, presumed to be embodied in thejust discovered chrom osom es, by unequal m itoses. The m achin-ery was supposed to allow organ and tissue-specific determ i-nants to be allotted to the respective parts of the developingbody in a predeterm ined, rig id order.

It was indeed a landm ark in Developmental Biology when theyoung Hans Driesch, one of the first to start experimenting onern bryo s (in 1891/92). noticed a surprising result: "I shook thegerrns [of the sea-urchin] rather violently during their two-cellstage, and I succeeded ...in separating the tw o blastom eres fromone another...But things turned out as they were bound to do andnot as I had expected; there was a typically whole blastu la in m ydish next m orning, differing only in its sm all size from a normalone; and this sm all but whole gastrula was followed by a wholeand typical small p luteus-Iarva" (Driesch, 1907, p.61). Later heobtained not only one larva but tw ins and, by shaking laterstages, several dwari larvae from one and the same egg.

Driesch's conclusion, based also on the phenomenon ofregeneration , w as: Living beings are not machines, for nomachine divided into parts will give rise to several wholernachines, each of which replaces the m issing parts by self-gen-eration . U nd ere stim ating th e inte lligence a nd im agin ativeness offuture generations of engineers, he also m aintained that "in prin-ciple no m achine produced by chem ical and physical m eans canbe contrived as the basis of the events observed" (Driesch,1899. p.99) [Self-replicating machines. chernical and mechani-cal, do exist nowadays, at least on the drawing-board. Forinstance: R ebek, 1994]

In teaching students, recent lecturers instantly have at hand aseemingly sim ple explanation of w hy isolated daughter G ells or

*A dd ress for rep rints: Z oolog isch es In stitut, R uprech t-K arls.U niv ersitiit, IN F 2 30 , D -69 12 0 H eidelberg , G erm any . FAX: 6 22 1.5 44 91 3. e -m ai l: w .m u lle r@ s ir -i us.mgen . un i-He ide lbe rg .de0214-6282/96/$03.00()UiCPr~ssPrim"di"S,"lin


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22 \VA. M iillel'compounds in the cytoplasm . Jacques Loeb(USA) considered the nucleus as centre ofoxidation i n t h e cell. Hans Driesch, like oth-ers, ascribed a fermentative function in therelease of cascades of physico-chemicalreactions to the nucleus. "W e view thenucleus as a m ixture of ferment- like com-pounds..." (Driesch, 1894, p.88). How ever,ferments of those days were not yet theenzymes of our days, able t o 're co gn iz e'substrates and to 'direct' reactions by'selecting' a distinct reaction out of severalth erm od yn am ic ally p os sib le o ne s.

To understand the dawning of an immi.nent, silent revolution in science w e shouldbe aware that "information" and relatedterms, which are now among the most oftenused term s i n B io lo g y , w er e introduce d inscience only in the second half of our centu-ry. Today's biologists can hardly im agine aBiology without ( ge ne tic ) " in fo rmat io n", w it h-o ut (g en etic ) "c od e", w ith ou t "tra ns crip tio n"and "translation", w ithout "m essenger m ole-cules", "signals", "receptors", "sig nal trans-m ission a nd tra nsduction", w ith out antibod-ies that are able to "recognize" antigens,w ithout "contra!", "regula tion" an d "data pro-cessing".

Before the turn of the century there weresome speculations which sought to com-pare inheritance with memory. As early as1870, th e p hy sio lo gis t Ewa ld H erin g, knownfor his theories on colour vision, envisionedheredity as a kind of remembrance of all thathas happened to the species in the continu-ity of generations. Yet, the theory was pro-posed to account for the assumed inheri-tance of acquired characters. W hen AugustW eismann (1834-1914) refuted th is long-

debated notion, equating heredity with m em ory also appeared tob e o b so le te .

In the previous centuries and decades it was often the bestbiologists, such as W illiam Harvey (1578-1657), G eorges LouisL ec le rc B uffo n (1 70 7-1 78 8), C as pa r F rie dric h W olff (1 73 3-1 79 4),C arl E rnst von B ae r (1792 -187 6), Johanne s M Oiler (1801 -185 8),and Claude Bernard (1813-1876), who felt unable to share thecom mon reductionistic view that all biological phenom ena couldbe deduced entirely from (the then known) physical laws, andwho were inclined to go along with vita listic views. Their patronw a s A ris to tle .

F ig . 1 . August W eis ma nn (18 34-1 914) (oil painting). Photograph c ou rte sy o f P ro f. K la us S an de r.

pieces of a Hydra are capable of doing the same as the fertilizede gg : A c omple te d ev elo pmen t o ut o f p arts is p ossib le b ec au seeach cell is endow ed with the whole genetic inform ation.Oriesch, by contrast, took refuge with Aristotle and his term

entelechy. W hy?

The dawn of "inform ation" took place only in the sec-ond half of our centuryAt the turn of the century, careful investigations carried out

predom inantly in the lab oratories of G erm an scie ntists providedgrow ing evidence that chromosomes are the m aterial carriers ofinheritance. W alter Flemming in Prague and Kiel, EduardStrasburger in Bonn, R ichard Hertwig in M unich, O skar H ertwigin B erlin, and in pa rticular Theod or B overi in W urzb urg identifie dth e m ain c arrie rs o f in he rita nc e.

But what was a chromosome in 1891 and at the turn of thecentury?

It was an unknown molecular complex, presumably a con-tainer of ferm ent-like a ctivities w hich m ight interact w ith soluble

The A ristotelian so ul: fo rm , en ergeia, en telech eia andgene ti c informat ionNo personality has influenced occidental thinking m ore than

the ancient Greek philosopher and universal scientistA ristoteles, A ristotle (384-322 a C). A n enth usiastic zo ologist, hewas the first to describe the development of the chick in his trea-tise "O n the gen era tion of a nim als". E ssential th eoretical exposi-


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t i o n s on dev elo pmen t a r e also found in his writings onMetaphysica ('B ey ond physical sciences', 'B eyond n ature') andDe a nim a ('O n th e s ou l').In studying the developm ent of the chicken, A ristotle saw ani n it i a l l y f o rm l e s s w h i t e a n d y e ll o w m a t t e r , i n L a t i n m a t e r i a , t h eu n s tr u c t u re d s tu ff c o n tr i b u t e d b y t h e m a t e r = m o th e r . T h i s matterundergoes "morphogenesis" (his term !). In the m idst of th is form -b e c o m in g m a s s a " j u m p i n g p o i n t " , t h e b e a t i n g h e a r t , d e m o n -s t r a t e s t h a t s o m e k i n d o f p o w e r i s e x e r t i n g m o t i o n .What is the form in g principle? It is energeia ( 'e ne rgy ') , f rome n = i n , i n h e re n t , a n d e r g o n = w o r k . T h e G r e e k t e r m e r g o n h a s ad o u b l e s e n s e s i m il a r t o t h e E n g l i s h t e r m 'w o r k ' o r t h e G e r m a nt e r m A r b e i t , d e n o t i n g o n t h e o n e h a n d p o w e r e x e r t e d b y a m o v -ing agency or a human being, and on the other hand the producto f an art is t.As a s y n o n y m of e n e r g e i a A r i s t o tl e e v e n m o re o f t e nu s e d t h e t e r m e n t e / e c h e i a f r o m e n = ' i n h e r e n t ' , t e / o s : ' e n d , g o a l,a im ' , a n d e c h e i n = ' t o h a v e ' . D ev e l o p m e n t i s g o v e r n e d b y a p r i n -c i p l e w h i c h b e a r s t h e e n d i n i t s e l f a n d s h a p e s s t r u c t u r e l e s s m a t -t e r, s tr i v in g f o r a s p e c i e s - s p e c i f i c f o rm .

Energeia o r e n t e / e c h e i a a r e l i k e w is e t h e e f f i c i e n t a n d f i n a lc a u s e o f a l i v i n g b o d y . M o r e o v e r , ente/echeia a l s o d e n o t e s t h ef i n i s h e d w o r k . I n t h e l a n g u a g e o f t h e P l a t o n i c - A ri s t o t e l i a n -Scho la s ti c ph ilosophy , ma t te r i s mere d ynam i5= potentiality, th ef i n i s h e d f o r m i s energeia/ente/echeia= a ct u a l i t y , i s a c t u a l e x i s -t e n c e , i s s y n t h e s i s o f m a t t e r a n d i d e a .To r e a c h a d e f i n e d s p e c i e s - s p e c i f i c e n d , t h e f o r m in g p r i n c i -p l e m u s t h a v e a "p re -exi st ing i dea" o f t h e f i n a l o u t c o m e ." N a t u ra l p ro d u ct i o n i s l i k e a r t i f i c i a l ; t h e s e e d o p e r a t e s l i k e t h os ew h o w o r k b y a r t - . A n d " a r t i s t i c p r o d u c t i o n p r e s u p p o s e s th epresence of form of the product in the soul of the artist."(M eta ph ysic a II, e d. b y w .o . R oss , 1 92 4,2 .7 .1 03 2-2 .9 .1 03 4).H e n c e , i t f o l l o w s t h a t t h e f i n a l energeia o r ente/echeia i n d e v e l-o p m e n t is the soul.

In the generation of m an, it i s - thus Ar is to tl e - the female par-e n t w h o c o n t r i b u t e s t h e v e h i c l e o f t h e s p e c i f i c f o r m . T h e m a t t e rcapable of adopting this specitic form is found in the surplusb l o o d . I t i s t h e m a l e p a r e n t w h o s e s p e r m c a r r i e s t h e s o u l , w h i c hw ill im pose the specific form on the fem ale m atter. (In a fem alechild the specific nature of the m ale parent is reproduced but isem barrassed by the inferior m atter w ith w hich it has to cope!).Thus, the soul is the means to all vital power and life. The liv-ing bo dy acq uires all its attribu tes by v irtue of so ul. H ow ever, th eso ul d isp la ys g rad atio n. Its lo we st fac ulty is th e v eg etativ e= n utri-t i v e p o w e r , h ig h e r f a c u l t i e s a r e s e n s a t i o n s , a p p e t i t i v e , i m a g in a-t i v e a n d i n te ll e c t u a l p o w e r s .

A r i s t o t l e in Deanimal i t e ra ll y : M T h e v eg e t a ti v e s o u l b e l o n g s t oo t h e r l i v i n g t h i n g s a s w el l a s t o m a n , b e i n g t h e f i r s t a n d m o s tw id e l y d i s t r i b u t e d f a c u l t y , i n v i r t u e o f w h i c h a l l t h i n g s p o s s e s sl i f e " . "Nowthe sou l i s cause and origino f the body ." " .. .f orthes o u l i s t h e c a u s e o f a n i m a t e b o d i e s b e i n g i n i t s e l f t h e o r i g i n o fm o t i o n , a s f i n a l c a u s e " . " Q u a l i t a t i v e c h a n g e , a l s o , a n d g r o w thare due to soul". "...nothing devoid of soul has sensation. Thesame holds of growth and decay". " T he nutritive faculty o f th esoul b e i n g t h e s am e a s t h e r e p ro d u ct i v e ".MItth e sou l} cau ses the produc ti on .. . o f another individual l ikeit. Its e sse ntia l n atu re a lre ad y e xists . ...it o nly main ta in s its e xis-tence. H e n c e t h e . . . p r i n c i p l e o f t h e s o u l i s t h e p o w e r t o p r e s e r v ei n e x i s t e n c e t h a t w h i c h p o s s e s s e s i t i n s o f a r a s i t i s a d e f i n i t ei n d i v i d u a l " .

History: from soul to i,{{ormatiol1 23

F ig . 2 . H an s D rie sc h (1 86 7.1 94 1) . P ho ro gra ph c ou rtes y o f P ro f K la us S an der .

"The p rimary soul is th at whic h is ca pable o f repro ducin g thespecies" (D e anim a, 416 b1-416 b27).The entelechy of the vitalist -Hans D rie sch-E ntelech y ha s ruled the individua t m orpho genesis of the gen-

e ra tio n whi ch is regarded as th e sta rtin g p oin t fo r in he rita nc e,and will rule a/so the m orphogenesis of the generation w hich ist o f ol low" (D ri es ch 1 90 8, p .2 27 -2 28 ). "Entelechy thus proves tobe also that which may be said to lie at the very ro ot o f in her i-tance." (D riesch, 1 907, p. 226 ).Driesch emphasizes a g a i n a n d a g a i n t h a t h i s e n t e l e c h y i s n o ta v i t a l i s t i c " f o r c e " ; i n s t e a d h e d e f i n e s i t a s " i n t e n s i v e m a n i f o l d -n e s s M and a s s o c i a t e s t e r m s s u c h a s ~ o r d e r " a n d - k n o w l e d g e ~w ith it. Entelechy selects betw een all the therm odynam icallyp o s s i b le r e a c ti o n s , t h u s c r e a t i n g M e x t e n s i v e m a n if o ld n e s s ", t h a ti s o rd e r e d c o m p le x i t y .

H o w e v e r , i n h i n d s i g h t D ri e s c h m a d e s e v e r a l s e v e r e m is t a k e sth at m ad e h is e nte le ch y u na cce pta ble :(1) Entelechy w as thought to be im material and not m ediatedby a physical carrier. O ne m ight sophistically discuss at lengthw h e t h er i n fo rm a t i o n a s s u ch , o r l i k e w is e n eg en tr o py , i s m a t e r i a l ,a n d w h a t M m a t e r i a l M i s a t a l l . ( T h e t e x t b o o k s i n p h y s i c a l s c i e n ce sd o n o t h e s i t a t e t o c l a s s i f y a p p a r e n t l y m a s s - l e s s p h e n o m e n as u c h a s m a g n e t i c f i e l d s or e l e c t r o m ag n e t i c w a v e s a s i m m a t e r i -a L) Wha te ver th e o utc om e, it is s im ply a fa ct tha t ge ne tic infor-mationis c a rr ie d b y m a c ro m o l e c u le s .


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24 \IIA. M iiller(2) Though entelechy does not reside in space, it acts in and

into space. And although Oriesch emphasizes that entelechy isnot a force, it is able to direct material events by "suspend ing"physical torces. W ith respect to the laws of energetics, he says:" Entelechy, as endow ed w ith the faculty of enlarging the am ountof diversity..." And: 'The work of the "demons' of Maxwell is herere ga rd ed a s a ctu ally accom plish ed ' (D riesch, 1908, p .225. ). LikeM axw ell h im se lf, D rie sch did n ot rea lize th at th ese dem ons w ouldhave to spend or consume some energy to obtain inform ation onthe kinetic energies of the m olecules. Apparently, D riesch did notconvince any of the renow ned contem porary physicists.(3) Driesch's entelechy grew to a universal entity just like thesoul of Aristotle. It governs life in all its qualities. In its m anifes-ta tio n a s .p sycho id -. e nte le ch y too k ove r a ll th e va riou s fu nctio nsof th e A risto te lian so ul.

Like the soul of Aristotle, the entelechy of Hans Drieschbecam e a source of universal inform ation capable of governingall that could not be explained in the term s of contem porary sci-ence. In developm ent, entelechy had to cover all kinds ofendogenous inform ation, regardless of the source of the respec-tive inform atio n an d its fu nctio na l co nte xt (se e be lo w .p ositio na linformation-).

It was Biology at the turn of the century, as it arose inGermany and the USA, which began to subdivide and to resolvethe com plex of sources of inform ation at w ork in developm ent.The three internal sources of information

W e now have to distinguish three sources of endogenousinfo rm atio n, (1 ) th e g en etic in fo rm ation encoded in the DNA o fth e n uc le us and the m itochondria, (2) maternal cytoplasm icinfo rm atio n w hich is d irectly (a lw ays? ) d erived from g en etic in fo r-m ation, (3) epigenetic inform ation acquired by the interaction ofth e ce lls. A t th e la tte r, sup ra ce llu la r le vel o f o rg aniza tio n g ene ticin fo rm ation is o nly in directly in vo lve d. a s it p ro vide s th e po ssibil-ity to produce signal m olecules, receptors, signal transducingsy ste ms a nd u ltim ate ly tra ns crip tio n fa cto rs ,Genetic informat ion

A few years after Driesch's epochal experiment, TheodorBoveri (1904a) was able to deduce the Mendelian rules from thebehaviour of the chromosomes in meiosis. He predicted the cou-pling of the genes in groups according to the number of chro-mosomes in the haploid state of a germ cell, a prediction laterverified by a friend of Driesch, Thomas Hunt Morgan (USA). Butit was only in the second half of our century when the primary'semantics' of the genetic code, its role in determ ining thesequence of bases in the various types of RNA and. hence, ofthe am ino acids in p oly pe ptid es , w as re ve ale d.Th e cyto pla sma tic d et erm inan ts (ma te rnal i nfo rma tio n)F ro m th e e arly b eg in nin g o f e xp erim en ta l e mb ry olo gy a tte n-tion w as directed tow ards intim ate cytoplasm atic inhom o-g en eitie s th at w ou ld e nd ow th e c ells re ce iv in g th em w ith d iffe r-e ntia l disp ositio ns for pa rticula r d evelo pm enta l p athw ays.Careful observations and subtle surgical interventions byWilhelm Roux, Theodor Bover i, Edmund B . Wi lson and ThomasH un t M org an le d to th e view tha t th e m orp ho ge netic po te ncie sa re n ot u nifo rm ly d is trib ute d in th e c le av in g e gg . W ilh elm R ou x,

one of the first to recognize the suitability of the m itotic appara-tus to enable an equal distribution of the hereditary m aterial, alsodiscussed the possibility of unequal m itoses as a means byw hich 'organ-form ing territories' m ight be established (Sander1991b, and references therein). The hypothesis of differentialm itoses had been a central notion in the innovative but highlyspeculative theories of August W eismann (Sander, 1991, an dr ef er ences t he re in ).

The clue to the existence of two separate sources of devel-opmental potencies was found in studies of the utmost m inute-ness carried out in the USA and Germany,(1) In the school of Edmund B. W ilson careful and patientobservations of spiralian em bryos not only led to the establish-m en t of d efin ed 'cell lineages' but also to the singular observa-tion that in the cleaving egg of the marine mollusc Oentalium thev eg eta l lo be (th en "y olk-sa c") does not contain a nucleus. Theremoval of this lobe nevertheless led to larvae lacking the mes-enchym e (E.B. W ilson, 1896, and references therein).(2) By observing disperm ic eggs, and later by centrifuginguncleaved eggs, Theodor Boveri (1904b, 1910) show ed that inthe nematode Parascaris graded cytoplasm ic qualities deter-m ine whether a cell enters the pathway to becoming a somaticcell (w hich exhibits the phenom enon of chrom atin dim inution) ora prim ord ia l g erm ce ll (w hich re ta in s th e co mp le te chrom atin ).

It also w as Theodor Boveri (191 O b) w ho introduced the gradi-ent hypothesis (Also: Sander, 1993, and references therein). Ase arly a s 1 90 2 B ov eri h ad e nv is io ne d .th at th e s im pte d iffe re nti-ation of the cytoplasm serves to set in motion the machinewhose essen tia l a nd p robably most c omp le x mechan ism re sid esin th e nuc le us . "W he n after the sev ere co lla pse d uring an d b etw ee n th e tw ow orld w ars G erm an D evelopm ental B iology began to revive, theidea of gradients w as resum ed (for instance: Sander, 1976, andreferences th erein) an d found its final verification in the dem on-stration of the bicoid gradient b y C hristiane N usslein-V olharda nd h er c ow or ke rs _ T he b ic oid p ro du ct s m u tu ally lin ke d g en eticin fo rm ation w ith th e cyto pla sm atic d eterm in ants: O n th e on eh an d, t he b ic oid d ete rm in an t is d er iv ed fr om th e m a te rn al b ic oidse le cto r g en e a s its m RN A co py , on the o th er ha nd its tran sla-tio na l p ro du ct. th e B IC O IO p ro te in , is a t ra ns crip tio n f ac to r c on -tro llin g se ts o f su bordin ate, 'zygo tic' ge ne s in th e de ve lo pin ggerm . Since this im portant discovery was published (e.g.NGsslein-Volhard e t a l. , 1 98 7) th e n um b er o f id en tifie d c yt op la s-m atic determ inants derived from m aternal genes is grow inga lmost month ly.A cquisition of new inform ation by cell interactions: posi-tio na l in fo rmatio n a nd in du ctio n in multic ellu la r s ys tems

T he th ird le ve l a t w hich in form atio n g ove rns p atte rn fo rm atio n,ce llu la r d iffe re ntia tio n, m orph og en esis a nd th e w ho le co mp le x o fself-organization, is the level of cell interactions or cell society.For the sake of simplicity, the paradigm of posi tiona l informationsh all stan d fo r th is leve l (w hich , h ow eve r, a lso co mp rise s che mo -taxis, transm ission of non-spatial inform ation by m itogenic fac-tors, h orm one s a nd n ervo us co nd uction ).

It was once more Hans Driesch who first recognized the phe-nomenon explicitly when he wrote his Fundamentalsatz (funda-m enta l statem en t, th eo rem ): "The prospective significance ofeach blastomere {the fate of a cell] is a function of its position in


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~.F ig . 3 . W i lh elm Roux ( 1850 -1924) . Photograph courtesy o f Pro f. K lau s Sander .

H isto ry : .1 ;'0 11 1soul to information 25Tubularia: the dependence of the fate ofevery element on the actual size of the sys-tem."

When Lewis W olpert independentlyrevived th e ide a of positio nal inform ation heused a remarkably sim ilar terminology:"spe cification", "positional value" instead of" pr os pe ct iv e v alu e" .

Yet, there are also differences betweenthe concepts of W olpert and Driesch. W hileW olpert derives positional inform ation fromgradients, Driesch in his early writingsdeveloped a c oncept of in ductive interac-tions. Years before Spemann, Drieschattributed positional effects to the follow inglis t o f fa ct or s:1 . M a ss -in du ctio n [ me an in g cytoplasmic fac-tors]2. Induction by tension and pressure3 . C on ta ct in du ctio n4 . C he mic al in du ctio n5. Induction by chem ical orientation [i.e.chemotaxis)6 . E xt er na l in du ctio n.

But, instead of starting the analysis of theproposed factors, Driesch deviated into thesphere of m etaphysics, assigning the finalcontrol over all physico-chem ical events tohis entelechy. By doing so, he discreditedthe w hole topic.By contrast, in the writings of W olpert,there was never a doubt that he was speak-ing of natural, epigenetic phenom ena w hichcan be understood and analyzed by physi-co-chem ica l m ean s, sup ported by com putersim ulations. T herefore, h is type of approachw as fruitful an d w ill b e contin ued.Di fferen t persona li ti es may contributeto com m on scientific concepts

In the realm of Biology, we cannot point to one single geniuswho had developed the concepts o f to da y's DevelopmentalBiology. The emerging concepts are the resultant of commonand diverging thoughts expressed by personalities so differentas Hans Driesch and Theodor Boveri.

H ere the colourful eloquent cosm opolitan, gifte d w ith unlim it-ed self-confidence and even an attitude of arrogance, rather cur-sory in his observations and in his sketches, but also endowedwith a highly imaginative, ingenious spirit. H is soaring m ind,however, drove him into that sphere which in the Germ an acad-em ic w orld and cultural tradition w as always valued m ore highlyth an n atu ra l s cie nc es : p hilo so ph y.

O n the other hand, his counterpart, the 'provincial' zoologist,s hy , s cru pu lo us , p erfe ctio nis tic , e xtre me ly c are fu l in h is o bs erv a-tions and experiments, documenting them with superb, exactdraw ings, but also endowed with a highly astute spirit.

S cience can integra te all pe rsona litie s d evote d to the search fo rt ru th , irr es pe ct iv e o f t he ir p ec ulia r c ha ra cte rs a nd th eir n at io na lit ie s.

t he who le " (D riesch, 1894). This is not his only statem ent on thistopic. A whole booklet was devoted to this phenomenon(Driesch, 1899). Only a few expositions, written in English byhimself in "Science and Philosophy of the Organism: G iffordLectures 1907" (published in 1908) m ay be quoted:p. 10 1:. ."that each single elem entary p rocess or developm entnot only has its specification, but also has its specific and typicalplace in the w hole - its locality".p. 127: In the hydroid Tubularia "you may cut the stem at what.ever level you like: a certain length of the stem will always restorethe new head by the co-operation of its part. As the point of sec-tion is of course absolutely at your choice, it is clear ... that thep ro sp ec ti ve v al ue of each part of the restoring stem is a "functiono f i ts pos it io n " , that it varies w ith its distance from the end of thes te m."... "B ut a lso th e s ec on d p oin t...c an b e d em on stra te d in


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