21 



ved en udlmgtnino' af peiibranchialsækken. Der er altsaa 

 bos de forskjellige familier forskjellige organer, hvorfra knop- 

 dannelsen kan udgaa. Dette har allerede for hengere tid 

 siden fort Giard til at opstille b knoijskydiiingsmodi. nem- 

 lig en (19): 



Bladogciiese imlJéale (Botryllidæ). 



Blastogénése stoloniale (Clavelina. Perophora. Polycliiiida'). 



Blastogr)ie»e pijloritiue (Distaplia). 



Ser man foreløhig bort fra denne forskjellighed i dan- 

 nelsen, anlægget af knopperne hos de forskjellige familier, 

 og studerei- man grundigere knopanlæggets formforhold, 

 anatomi, da viser denne hos alle grupper saa store over- 

 ensstemmelser, at knopskydninger overalt paa det tydeligste 

 viser sig at være en og den saunne udviklingsmodus. Hos 

 alle grupper bestaar nemlig det unge knopanlæg af to con- 

 centriske, blæreformede epithelmembraner, af hvilke altsaa 

 den ene (den ,.ydre") omgiver den anden (den ,,in(lre"), og 

 mellem hvilke der desuden vandrer mesodermale elementer 

 iud fra moderdyret. 



Medens nu knoinmlæggets ydre blære overalt dannes 

 af moderdyrets hud, epidermis, saa frembyder den indre 

 blæres dannelse den eiendiMnmelighed, at den hos forskjel- 

 lige familier anlægges ud fra forskjellige organer. Efter 

 den foreliggende Ascidielitteratur har det da vist sig, at 

 den indre blære bos knopperne af 



Distaplia,'*) 



Pyrosoma samt 



Abdominalknoppen hos Dideiiniidenie 

 hos 



Amarouciain 1 fra postabdomens 



Polj/cliuiiiii o s.v. j 

 hos 



Peropliora \ 



Clavelina j 



dannes fra 

 Tarmtraktus. 



ikillevæg. 



fra stolonernes 

 skillevæs. 



fra epicardiet. 



altsaa fra epi- 

 cardiet. 



I fra peribranchial- 

 I sædcken. 



hos 



Thoracalknoppen | 



hos Didemnidernei 

 hos 



BoinjUiderne 



Polysfyeliderne 



Skjont altsaa, som ovenfor n;evnt. knopanlæggets indre 

 blære overalt viser den samme bygning og overalt spiller 

 den samme rolle for knoppens organdannelse, saa tinder det 

 eiendommelige forhold sted, at bilæren hos en grupjje kan 

 anlægges fra tarmtruhtus, hos en anden fra epicardiet. hos 

 en tredie fra peribrancJnalsæJikeii. 



Dette — nu almindelig anerkjendte faktum har freni- 

 Inidt store theoretiske vanskeligheder for alle dem, der har 

 studeret Ascidiernes knopskydning. Man har havt den faste 

 formening, at alle dannelser, der viser samme bygning og 

 funktion ogsaa maa anlægges paa sannue maade og nd fra 

 samme ..materiale". Det har da især vakt tvivl, at to saa 

 forskjelligartede organer som tarmtraktus og peribranchial- 



*) Under korrekturen er Julings ,,Reoherches sur la Blastogcnese 

 chcz Distaplia". Compt. Hend. des Séances du 3 cougi-. intern, 

 zool. 189.') kommen mig iliænde. Ifofge dette interessante arbeide 

 kommer knopperne lius Distaplia fra et epicardium. 



an evagination of the peribranchial cavity. There are thus 

 in the various families, various organs from which the bud 

 may originate. This led Giard (19), sonie time ago, to 

 establisli 3 ways of budding, viz: 



Blastoyé)ii'se palléah (Botryllidæ), 



Blastoyénese stoloniale (Clavelina, Perophora, Polyclinidæ), 



Blastogénése pyloriqiie (Distaplia). 



Tf. iudeiiendently of this difference in the formation 

 of the rudiment of the bud in the various families, we 

 study more carefidly the conditions of form, the anatomy, 

 of the incipient bud. it presents in all the groups such 

 great harmony. that budding is cverywhere most distinctly 

 proved to be one. and one only, mode of development; 

 (or in every group. the young incipient bud consists of two 

 concentric, vesicnlar, epethelial membranes, one of which 

 (the ,,onter-') surrounds the other (the ..inner"). and be- 

 tween which, mesoderm elements from the parent animal 

 also tind their way. 



Now whilo the outer vesicle of the incipient bud is 

 always formed from the epidermis, of the parent animal, 

 the peculiarity of tlie formation of the inner vesicle is, that 

 in different families it is developed from different organs. 

 According to the Ascidian literature now before us, it ap- 

 pears that the inner vesicle in buds of 



Dist((plia. *) and 



Pyrasoiiia. and 



Abdominal buds in Didemnida'- 



m 



in 



Aiuannicium 

 Pohjvliiniiii. etc. 



Perophora and 

 Clavelina 



Ifrom the sei)tum of 

 I the post-abdomeu; 



jfrom the septum of 

 I the stolons: 



in I 

 i 



from the epicar- 

 dium; 



are formed trom 



the alimontary 



canal. 



therefore from 

 the epicardium; 



Thoracic buds n 



Didenmidæ 

 and in 



Botryllidæ and Ifrom the perihran- 



Polystyelidæ i chial cavity. 



Thus although, as mentioned above. the inner vesicle 

 of the rudimentary bud always exhil:)its the same structure, 

 and always plays the same part in the formation of the 

 organs of the bud, the peculiar fact rcmains, that in one 

 group it may orginate in the alinæntary canal, in another 

 in the epicnrdimn, in a third in the peribranchial cavity. 

 This now generally-acknowledged fact has presented 

 great theoretical difficulties to all who have studied the 

 budding of Ascidiæ. The opinion, that all formations ex- 

 hibiting the same structure and function must also originate 

 in the same way, and from the same ..material", has been 

 tirmly held. Doubt has especially been aroused by the 

 fact that two such heterogeneous organs as the alimentary 



*) While this papcr was in the jwess, I fell in witli Julin's ,,Ee- 

 cheixhes sur la Blastogénése chez Eistaplia". compt. Rend. des 

 Séances du '6° congr. intern, zool. 189.'). Accoi'ding to this iu- 

 tercsting work, the buds in Distaplia come from an epicardium. 



