39 



gjælder det dannelsen af tarnitniktus og i)eribi\inchialsæk. 

 Nervesystemets og dorsalrørets dannelse ])liver imidlertid 

 uforstaaelig efter hans fremstilling. 



FizoJi beskrev dernæst (48 a) knopskydningen hos 

 Cirdnalinm concvescens og Atnaroucium aldeles overensstem- 

 mende med den frems;illing jeg ovenfor iiar givet af de 

 yngre stadier ved figurerne. pl. X, fig. 10 og 11. Han bo- 

 negter imidlertid bestemt at dorsalroret siden differentierer 

 sig i ganglion og „hypophysis". Han mener derimod, at 

 nervesystemet vokser ind i knop})en som en liden fin nerve- 

 streng, ,,cordoa nerveux ensbryonnaire". Han siger, pag. 

 128: ,,Chez ces deux espéccs, pas pins que ehez les Péro- 

 phores. le tulie ([ui constitue organe vi!)ratile embryonnaire 

 ne peut etre eonsidéré comme nu tube neural primitif, aiusi 

 (]ue r,i fait Kowalevsky. Ce i)rétendu tube neural do Ko- 

 walevsky se différencii' ultérieurement [)our produire Torgane 

 vibratile. qui n'a rien do nerveux, tandis qu'au-dessus de 

 lui se trouvo lo voritalilc cordon nerveux emliryonnaire." 



Da dette siJørgsmaal forekom mig af afgjørende be. 

 tydning har jeg ligesiden høsten 1892 stadig undersogt foi-- 

 skjellige Ascidieknopper og hos talrige grupper (Bofrtjlhts _ 

 Boirylloides, Glossopliorum, Disiaplia. Didemnum og Pijro- 

 soma) overbevist mig om, at gangliet virkelig afsnores. Jeg 

 maa derfor paa det bestemteste hævde den opfatning, at 

 dorsalroret virkelig er ,jlet fællcs anlæg for f/anglion og 

 liypopJtysis'' . I en foreløbig meddelelse til denne afliand- 

 ling (33) gjorde jeg opmerksom paa, at heller ikke Pizon 

 forniaaede direkte at paavise den nervetraad der skal vokse 

 ind i knoppen fra moderdyret. Dotte væsentligo punkt 

 hviler derfor i)aa theoretiske opfatuinger. og imodsa^tuing 

 hertil staar mit positive fund, at gangliet virkelig snorer 

 sig af fra dorsalroret. 



Min forolobige meddelse har faaet en bekræftelse af 

 Hore forskere, idet Caullery, Bitter og Lefivre hos forskjel- 

 lige grupper noiagtig har iagttagot det samme. 



Botragter man nu knopskydningen hos de forskjellige 

 familier fra et sammenlignende synspunkt, saa forekommer 

 det mig, at der nu foreligger et saa stort materiale, at det 

 maa være tilladt at drage almindeligere slutninger. Det 

 synes fremdeles, at saavel knopanlægget som organudviklin- 

 gen hos alle grupper fi-embyder saa store overensstemmelser, 

 at det bliver os muligt i de vigtigste træk iallefald at op- 

 stillo et almindoligt 



Sclieiiia 



for orgauudviklingen hos kuopperne. 



1) Dette schomas første og vigtigste lov er den, at knop- 

 anlæggets ydre blære lam leverer laioppens epidermis, 

 medens edle andre orgamr dannes af den indre hlcere 

 og af de vandrende mesodormceller. 



to tho formation of tho aliraentary canal and the peribran- 

 chial cavity. The formation of the nervous system, how- 

 over, and of the dorsal tube are incomprohensible according 

 to his account. 



Fizon next doscribed (48 a) l)udding in Circinalimn 

 roncrescens and Amanniriiim, in perfoet iiarmony with tho 

 account I have given above of the earlier stages on Pl. X, 

 figs, 10 and 11. He positively denies, however, tliat tho 

 dorsal tube is afterwards differentiated into ganglion aud 

 ,,hypophysis-'. He thinks, on tiie other hand, that thr 

 nervous system grows into the bud as a small, fine nerve- 

 c.ord, — „cordon nerveux ejnbryonnaire". On p. 128, he 

 says: ,,Ohez ces deux espéces, pas plus quo chez les Pé- 

 rophores, le tulje (]ui constitue rorgaut- viliratile embryon- 

 naire ne peut étre cnnsidéré comme un tube neural primitif 

 ainsi que l'a fait Kowalevsky. Ce prétendu tube muiral 

 de Kowalevsky se différencie ultérienroment pour produire 

 Torgane vibratile, (jui n'a rien de nerveux, tandis qu'au- 

 dessus de lui se trouvo le veritable cordon nei'veux em- 

 bryonnaire.-' 



As this question appeared to me to be of decisive 

 iniportance, I have, ever sinco tlie autunin of 1892, made 

 froquont examination of various Ascidian buds, aud in 

 numerous groups (BotrijUiis, Botrylloides, GlossopJiorinn. 

 DiMapIia, Dideinnion and Pgrosonia). convincod myself 

 that the ganglion is actually constricted. I must thorofore 

 most positively maintain the theory that tho dorsal tube 

 is really the ,,comnion rudiment oj the ganglion and the 

 hgpophgsis" . In a statement preliminary to this treatise 

 (33), I drew attention to the fact that Pizon was also 

 unablo to show diroctly the nerve fibre which was said to 

 grow into the bud from tho pai-ent animal. This essential 

 l)oint rests theroforo upon theoretical opinions, and in op- 

 position to it stands my actual discovery, that the ganglion 

 is really constricted from the dorsal tube. 



My preliminary statement has received confirmation 

 from several naturalists, Caullery, Bitter and Lefevre having 

 carefully observod the same thing in different groups. 



If budding in the various families be regarded from 

 a comparative point of view. it appears to me that we 

 now have so much material, that we may be permittod to 

 draw general conclusions. It seems moreover tiiat both 

 the bud rudiment and the development of the organs pre- 

 sent such great similarity in all the groups, that it will 

 be possible for us, at any rate in the most important 

 features to draw up a general 



Schedule 



for the Development of the Organs in the Bud. 



(1) The first and most impoi'tant law of this schodule is, 

 that the outer vesicle of the bud-rudiment onlg pro- 

 duces the epidermis of the hud, while all thf other 

 organs are fornied from the inner vesicle, and from 

 wandering mesoderni cells. 



