472 



TUNICATA. 



- - m s 



-- — #13 



^"U, 



not 

 de- 

 the 



(resulting from the fusion of paired strands) is assumed to be the 

 genital rudiment. The unpaired strand m is regarded as the rudi- 

 ment of the pericardial sac, 

 and the mass n, which from 

 the first is unpaired, as that 

 of the nervous system. 



The buds are produced 

 through the transverse con- 

 striction of the ventral 

 stolon (Fig. 243, r and st), 

 from which they eventually 

 become completely de- 

 tached. In structure, they 

 resemble the stolon itself, 

 being composed of an ecto- 

 dermal envelope and the 

 seven strands above de- 

 scribed. • They are 

 capable, however, of 

 veloping further on 

 ventral stolon. Gkobben 

 has therefore regarded the 

 ventral stolon, which is 

 evidently homologous with 

 the proliferating stolon of 

 thi' other Tunicates, as a 

 vestigial stolon, and con- 

 siders the buds produced 

 by it as abortive. 



A cross-section of the 

 dorsal outgrowth (Fig. 243, 

 st') of the " nurse " genera- 

 tion (hlastozooid) reveals 

 an essentially different 

 structure (Uljanin). Like 

 the ventral stolon, it is 

 covered superficially by a 

 layer of ectoderm, thickened 

 on the dorsal side, but the 

 interior of this outgrowth 

 is occupied merely by two 



u.' w- / 



Fig. 243. — Dorsal view of the posterior part oi the 

 body in a large " nurse " (blastozooid) Doliolum 

 .(after Barrois). /, lateral buds (gastrozooids) ; 

 in, median buds (phorozooids) ; ms^-ms'*, four 

 posterior muscle-hoops ; p, pericardium ; /'. 

 rosette-like organ ; st, ventral stolon ; st', dorsal 

 outgrowth ; u, primitive buds wandering to the 

 ventral side of the "nurse" ; //', primitive buds 

 wandering to the dorsal side ; n" , primitive 

 buds on the dorsal outgrowth. 



