25 



sig dannet ved afplatniiig af det oprindelige cylinderformige 

 epicardium. Knopanlægget dannes, som figuren viser, der- 

 ved at den ene lamelle bugtes ud og skyver den ydre cy- 

 linder, epidermis, foran sig, hvorved saavel epidermis som 

 skillevæggens iidbugtning snart antager den for knopanlæg- 

 get karakteristiske blæreform. 



Knopanlægget hos BotryUiderne ilUistreres af fig. 5 

 (Pl. IX). Man iagttager her, hvorledes paa dyrets venstre 

 og høire sider peribranchialsækken danner lignende udbugt- 

 ninger, der paa det i fig. 5 afbildede stadium allerede ty- 

 delig har antaget formen af blærer, og som snart næsten 

 helt afsnores fra moderdyret. 



Den i fig. 9, pl. XII, afbildede larve af Distajylia 

 viser knopdannelsen hos denne familie. Det er her tarm- 

 partiet nær æsophagus der ved udbugtning danner den 

 „indre blære-'. I cellulosekappen finder man desuden be- 

 liggende to allerede afsnorede knopper (kn). Af DeJIa 

 Valles og SaJenski/s undersogelser (13. 55) er det bekjendt, 

 at disse knopper formaar at formere sig ved deling. 



Ogsaa hos Pyrosoma dannes den indre blære, her. 

 ,.stolonen", hos knopperne (her tales ikke ora do fire første 

 men kun om de senere Ascidiozooider. Se foregaaende af- 

 handling) af entodermen. Efter SeeJiger (59) er pl. X, 

 fig. 1 afbildet et moderindivid med en yngre og en ældre 

 knop, og man iagttager, at „stolonens" indre streng, cylin- 

 der fortsætter sig i nioderdyrets tarmtraktus. 



Det er almindelig kjendt, at hos grupjjen Polyclinidæ 

 foregaar knopdannelsen derved, ar postabdomen deles i 

 flere 4 — 5 knopper. Efter Kowalevskys grundlæggende un- 

 dersogelser har jeg afbildet dette pl. X fig. 7 og 8. Den 

 indre blære fremgaar her direkte ved en afsnøring af epi- 

 cardiet postalidomens skillevæg paa tvers. Se forøvrig 

 Huitfeldt-Kaas's afhandhng, dette verk pl. I, fig. 7, hvor 

 det samme ogsaa er fundet for den af mig specielt under- 

 søgte Glossojihorum sabulosum. 



Disse grupper skal nu tjene som de vigtigste repræ- 

 sentanter for de forskjeUige former af Ascidiernes knop- 

 skydning. 



Knopanlægget er, som nævnt, overalt bygget af 2 

 concentriske epithelblærer, der udbugtes eller afsnøres fra 

 moderdyret; mellom disse blærer vandrer talrige mesoderm 

 — respektive generationsceller ind i knopanlægget. Blæ- 

 rerne har, hvor en udbugtning finder sted, forst halvkugle- 

 saa kugleform; denne bliver imidlertid overalt snart afiang, 

 hvorved dyrets senere længdeakse snart markeres. 



Den ydre blære, der som vi saa altid var en fortsæt 

 tolse af moderdyrets hud, epidermis, har overalt ogsaa epi- 

 dermis histologiske bygning, og knopskydningen finder intet- 



Den norske Nordhavsexpedition. Johan Hjort: Kimbladstudier paa 



must be imagined as formod by the flattening of the origi- 

 nally cylindrical epicardium. The rudimentnry bud is 

 formod, as the figure shows, by one lamella balging out, and 

 pushing the onter cylinder — the epidermis — before it, 

 thus causing the evaginations both of the epidermis and 

 the septum soon to assume the vesicular form charactoristic 

 of the incipient bud. 



The rudimentary bud in BotryUidce is illustrated in 

 fig. 5, Pl. IX. It will hore be seen how, on the rigiit 

 and loft sides of the animal, the j)eribranchial cavity forms 

 similar evaginations, which, in the stage represented in 

 fig. 5, have already distinctly assumed the form of vesicles, 

 and which are soon almost cntirely cut off from the parent 

 animal. 



The larva of Distaplia, represented in fig. 9, Pl. XII, 

 shows the formation of the bud in that family. Here, it 

 is that part of the intestine near the æsophagus, which, 

 by evagination, forms the ,,inner vesicle". In the cellulose 

 tunic. there are also two already constricted buds (kn). It 

 is well known from Ddla YalWs and Salensky's investiga- 

 tions (13, 55) that these buds are capable of propagation 

 by fission. 



In Pyrosoma too, the inner vesicle — here the „sto- 

 lon" — is formod in the buds (the first four buds are not 

 meant here, but only the later Ascidiozooids : see the pre- 

 ceding paper) from the endoderm. On Pl. X, fig. 1 is 

 represented. after Seeliger (59) a parent animal with one 

 young, and one older bud; and it will be observed that the 

 inner cord, or cylinder of the stolou is continued into the 

 intestine of the parent animal. 



It is generally known that in the group Polyclinidæ, 

 budding takes place by the division of the post.abdomon 

 into several — 4 or 5 — buds. I have drawn figs. 7 and 8, 

 Pl. X, from Kowalevskys fundamental investigations. The 

 inner vesicle here proceeds directly from a transverse con- 

 striction of the epicardium (the wall of the post-abdomcn). 

 See also Huiifeldt-Kaass paper in the present work, Pl. I, 

 fig. 7, whoro the same thing was found in a Olossoplionwi 

 sabidos^tm, spocially examined by me. 



These groups are now to serve as the most important 

 representatives of the different forms of budding in the 

 Ascidiaus. 



The incipient bud, as already mentioned, is always 

 constructed of 2 concontric opitholial vesicles, whicii are 

 evaginated or constricted from the parent animal; between 

 these vesicles, numerous mesoderm — as well as generative 

 cells find their way into the incipient bud. Where an 

 evagination takes place, the vesicles have first a hemisphe- 

 rical, and then a spherical shape, which always, however, 

 soon bocomes oblong, whereby the subsequent long axis of 

 the animal is marked. 



Tlie outer vesicle. which, as we have seen, is always 

 a continuation of the skin — epidermis — of the parent 

 animal, has also always the histological structure of the 



grundlag af Ascidiernes udvikling. 4 



