30 



les. Dorsalroret er bos DistapJia derfor eftev min mening 

 alligevel helt ud homolog med dorsalroret hos BotryUns. 



En helt anden sag vilde det være, om det viste sig, 

 at stolonernes skillevæg hos larven dannes fra periljranchial- 

 sækken. 



Botryllidæ. 



Kowalevshys videre undersogelser (38) gjaldt Disfaplia 

 og Amaroudnm. Han beskrev for disse grupper knopskyd- 

 ningens forlol) efter ganske det sannno skema, som jeg 

 ovenfor har fremstillet for Peropliora, og vi vil komme til- 

 bage hertil under disse grupper. De videre fremskridt paa 

 Ascidieknopskydningens omraade skyldtes dernæst studiet 

 af BotryUiderne, idet Pizon (48 a), Oka (45) og forfatteren 

 (31) uafhrengig af hinanden beskrev denne gruppes knop- 

 skydning og kolon idannelse.*) 



Knopperne anlægges hos Botryllus som nævnt i Kap. 

 1 fra Peribranchialsækken af, et forhold, som allerede Met- 

 scJuiihoff og Della Valle (13) tidligere havde konstateret. 

 Fig. 5, Pl. IX ser man de unge knopanlæg som 2 concen- 

 triske blæreforraige udbugtninger af epidermis og peribran- 

 chialsækken. Ogsaa her er, efter min fremstilling, det 

 hovedsagelig karakteristiske træk for knoppens udvikling det, 

 at den ,,ydre blære", epidermis, ingen anden rolle spiller 

 i udviklingen end, at den danner knoppens hud. Alle 

 andre organer dannes derfor af den indre blære og af de 

 vandrende mesodermelementer. 



Paa den indre blære iagttager man ligesom hos Pero- 

 plioraknoppen snart 2 sagittale folder, der her dog kun op- 

 træder fortil og ventralt, saa at den indre blære efterhaan- 

 den deles i en midtre blære, der bagtil og dorsalt stanr i 

 forbindelse med de 2 laterale blærer (anlægget til peribran- 

 chialsækken). Se fig. 6 og 7 pl. IX. Et tversnit gjennem 

 knoppens bagre parti giver os paa det i fig. (J afljildede 

 stadium hosstaaende figur 



investigations, from the raiddle of the 3 vesieles into which 

 the inner vesicle is divided. The dorsal tube in Disfaplia 

 is therefore, in my opinion, entirely homologous with the 

 dorsal tube in Botryllus. 



I would be another matter altogether if it turned out 

 that the septum of the stolons in the larra was formed 

 from the peribranchial cavity. 



Botryllidæ. 



Koicalersky's further investigations (38) liad reference 

 to Distaplia and Amaroucium. He described the course 

 of budding in these groups acccrding to exactly the same 

 plan as I have given above for Perophora. and we will 

 return to it when discussing these groups. Furtlier pro- 

 gress in the subject of Ascidian budding was duo to tlie 

 study of Botryllidæ, Pizon (48 rt), Olca (45) and the present 

 ivriter (31) having independently of one another described 

 the budding and colony-formation of this group.*) 



The buds in Botryllus originate, as mentioned in 

 Chapter II, in the pei'ibr:inchial cavity, a fact which Met- 

 scJr)uI,-off and Della Valle (13) had already demonstrated. 

 On Pl. IX, fig. 5, we see the young rudimentary bud as 

 2 concentric, vesicular evaginations of the epidermis and 

 the peribranchial cavity. Here too, according to my inter- 

 pretation, the most characteristic feature of the bud's de- 

 velopment is that the outer vesicle. the epidermis. performs 

 no other part in the devcl()])ment than that of forming the 

 skin of the bud. All the other organs are therefore formed 

 from tile inner vesicle and the wandering mesoderm elements. 



On the inner vesicle, just as in the Perophora bud, 

 may soon be seen 2 sagittal folds, which here, however. 

 only make their appearance anteriorly and ventrally, so 

 that the inner vesicle is divided by degrees into a middle 

 vesicle, whicli is connected posteriorly and dorsally with 

 the 2 lateral vesieles (the rudiment of the peribranchial 

 cavity). (See Pl. IX, rigs. (J and 7). A transverse section 

 through the posterior part of tlie bud gives us the accom- 

 panying figure in the stage rejjresented in fig. G. 



Fig. 8. Efter Hjort (3 li 



Ep = Epidermis, B-s = Branchialsæk, gjælletarm, Phc - 

 Anlægget til peribranchialsækken, D-ll = dorsalroret, Ov = 

 (3varier. 



Den videre udvikling afviger deri fra knopskydningen 

 hos Perophora, at peribranchialsækken ikke afsnøres som 

 2 sække, der siden igjen smelter sammen til et enkelt or- 

 gan. Derimod snøres peribranchialsæ'kken straks af som 



') Pizon s foreløbige meddelelse [46) var saavel Oka, som mig ube- 

 kjendt, bvad jeg for miu del meget beklager. 



IJj) = epidermis; i>-(S' = branchial sac, branchial gut; 

 Phc = rudiment of the peril)ranchial cavity; DR = dorsal 

 tube; Ov = ovaries. 



The further development difters fri)m budding in Pe- 

 rophora in that the peribranchial cavity is not constricted 

 as 2 sacs which subsequently again coalesce into one organ. 

 On the contrary, the peribranchial cavity is constricted im- 



*) Pizons preliminary account (lli) was unkiiown both to Oka and 

 myself, a circumstauce which I, for my part, rauch regret. 



