472 



TUNICATA. 



(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 

 scribed. They 



de- 

 not 

 de- 

 the 



FIG. 243. Dorsal view of the posterior part of the 

 body iu a large " nurse " (blastozooid) Doliolwii 

 (after BARROIS). I, lateral buds (gastrozooids) ; 

 in, median buds (phorozooids) ; msP-msP, four 

 posterior muscle-hoops ; p, pericardium ; r, 

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

 outgrowth ; u, primitive buds wandering to the 

 ventral side of the ' ' nurse ' ' ; n', primitive buds 

 wandering to the dorsal side ; u", primitive 

 buds on the dorsal outgrowth. 



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 

 the 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 (blastozooid) 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 



