60 



provoquer les phcnoinénes de la vie, agir sui- eiix. les niodi- 

 iier, ce ivest pas å la force vitale*), entité insaisisable, qu'il 

 liii faudra s'adresser, mais aux conditions physiques et 

 chiniiques qui eiitraineiit et commandeut la. inanifestation 

 vitale." Saaledes bor efter min formening ogsaa spørgs- 

 maalet om ciaigenesis eller evolution i ndviklingen alene 

 besvares ved undersogelser over, hvorledes ndviklingen for- 

 holder sig til bestemte morphologiske begreber, som celler, 

 kimhlade, organer o. s. v. 



Fra dette synspunkt er Ascidiernes knopskydning som 

 al udviMing epigenese. Knopskydiiingen begynder nemlig 

 med et anlæg, der ikke viser nogen af Ascidiernes organer 

 eller kimblade, men som derimod bestaar af et lidet antal 

 celler, der ved complicerede processcr danner det voksne 

 dyr. Betragter man mi ndviklingen som reaktioner paa 

 j.Reize-'. saa maa man antage at anlæggct oprindelig har 

 udviklet sig som del af et af moderdyrets organer, men at 

 det da undi-r ndviklingen har erholdt en impuls til udvik- 

 ling i anden retning. Hos Botryllideriie er saaledes cel- 

 lerne i knopanlæggets indre blære først en del af moder- 

 dyrets peribranchialsæk, indtil de sondrer sig ud fra denne 

 og danner et andet individ. At fremdeles andre forhold 

 og Eeize ogsaa maa finde sted under knoppens ndvikling 

 fremgaar deraf, at denne forlober anderledes end i emln'yo- 

 nalud viklingen. Saaledes n;evntes ovenfor at knopanlæggets 

 ydre blære ikke formaar at danne andet end Ascidiens 

 epiderniis, og at f. eks. nervesystemet fremgaar af den 

 indre blære. Ogsaa dette viser bestemt: 



1) At forandrede forholil („Reize") formaar at forandre 

 udviklingens forlob. 



2) At organismen formaar under andre torliold paa anden 

 maade at danne den ene og samme formdannelse (arts- 

 typen). 



Det vil utvivlsomt være forkastet at soge at paa vise 

 hvilke forandringer i anLægget der fremkalder forandringer 

 i udviklingens forlob. Man kan kun lier udtale sig med 

 den største forsigtighed. Jeg har ovenfor nævnt at den 

 omstændighed at knopjiens ydre blære Ijestaar af en difife- 

 rentieret epiderniis maa antages at raodificere knopskydnin- 

 gen. Paa den anden side nævntes, at entodermen hos 

 Ascidieæggene antagelig paavirkedes i sit forhold ved ile 

 store mængder blommemasse, der i enkelte grupper (Dtda- 

 plia) kom til ndvikling, en tanke som Balfour forlængst 

 har udtalt for Teleostieræggenes vedkonnnende. 



Saadanne eksempler formaar imidlertid alene at an- 

 iijde en enkelt faktor og de er utvivlsomt alene den forste 

 famlende begyndelse til opfatniuger og erfaringer, som en 

 fremtidig videnskali vil ln'inge til en anden klarhed. 



*) Ordet ,.Livskrafteu" involverer ikke lier ligesaalidt som hos 

 Claude Bernard nogensomhelst metafysisk opfatniug, men er 

 alene et navn paa det metafysiske problem. 



provoquer les phénomenes de la vie, agir sur eux, les mo- 

 ditier, ce n'est pas a la force vitale*), entité insaisissable, 

 qu'il lui faudra s"adresser, mais aux conditions physiques 

 et ehimi(pics qui entrainent et commandeut la manifestation 

 vitale." In my opinion, should one attempt to elucidate 

 the question of epigenesis or evolution in development, by 

 nothing but investigations as to the relation of the deve- 

 lopment to certain morpliological conceptions. such as cells, 

 gerni-hiyers, organs, etc. 



From this point of vie\v. the Inulding of Ascidians, 

 like all drrclopinent is epigenesis. Budding begins with a 

 rudiment whicli shows none of the Ascidian organs or germ- 

 layers, but which, on the contrary consists of a small 

 numlier of cells, wliicli. by comj)licated jjrocesses, form the 

 adult animal. If the develojunent l)e considered as reaction 

 on ..Reize", we must presume that the rudiment has ori- 

 ginally developed as part of one of the organs of the pa- 

 rent animal, but that during development it has acquired 

 an impulso to develope in another direction. Tluis in 

 Botrgllidw. the cells in the inner vesicle of the bud-rudi- 

 ment are at first jiai-t of tiie peribranchial cavity of the 

 pai-ent animal, uutil they separate from it. and form an- 

 other animal. That yet other conditions and „Reize" may 

 also occur during the develojnnent of tlie bud, arises from 

 the fact that that development takes a different course to 

 that of the embryonie development. In this way it has 

 been inentioned above that the outer vesicle of the bud- 

 rudiment is only capable of forming the Ascidian's epiderniis, 

 and that. e. g. the uervous system proceeds from tlie inner 

 vesicle. This, too, shows decidedly: 



(1) Tliat altered conditions (,,Reize") are capable of al- 

 tering tlie course of the development; 



(2) Tliat under other conditiims the organisni is capable 

 of forming, in another way, the same form-formation 

 (type of the species). 



It would without doulit be premature to attemjit to 

 demonstvate wiiat are the changes in the rudiment, whicli 

 produce changes in the course of the development. It is 

 only with tiie greatest cautiou that oiu^ can express an 

 opinion. I have stated above that we must presume that 

 the budding is modified by the circumstance that the outer 

 vesicle of the Inid consists of a differentiated epiderniis. 

 On the other hand, it is stated that the endoderm in Asci- 

 dian ova is probaldy affected in its conditions by the great 

 quantity of yolk which was developed in certain groups 

 (Distaplia), a thought which Balfoar has longe since ex- 

 pressed with regard to the ova of Teleosteans. 



Such instances, however, can only indicate a single 

 factor. and are doubtless only the first uncertaiu coramence- 

 ment to the comprehension aud experience wliich future 

 science wil! can'v on to a diflerent desree of clearness. 



*) Xeither here nor as used Ijy Claude Bernard do the \vord.s 

 ,,1'orce vitale" exjiress any metajjliysical view; they are mercly a 

 uame for the raetaphysical iirolilem. 



