476 TUNICATA. 



dorsal outgrowth of the "nurse," and carries the buds of the sexual 

 generation or gonozooids (</). The latter was formerly thought to be 

 produced from the phorozooid itself, and these buds, when free, were 

 consequently known as the second "nurse" generation. The sexual 

 generation, however, is produced from a primitive bud which has 

 become attached to the base of the peduncle of the phorozooid. This 

 bud, according to Uljanin, is not yielded by the phorozooid itself, 

 but is a direct descendant of the primitive buds (Fig. 243, it") which 

 wandered over to the dorsal outgrowth of the first "nurse" genera- 

 tion. Uljanin therefore regards the median bud merely as the foster- 

 mother of the buds which develop into sexual animals. 



There is thus, according to Uljanin, in the whole cycle of genera- 

 tions of Doliolum, only a single true proliferating stolon, viz., the 

 ventral stolon, which alone is capable of producing primitive buds. 

 All the individuals derived from these primitive buds which attain 

 development represent, according to this author, only the hetero- 

 morphous forms of one and the same generation, the sexual genera- 

 tion either, as nutritive animals or as foster forms, losing their genital 

 organs, or else changing into actual sexual animals (Fig. 245 C). 



According to Gbobben, on the contrary, who practically follows 

 Gegenbatjr, the cycle of generations of Doliolum consists of two 

 successive asexual generations and one sexual generation. Grobben 

 consequently regards the form yielded by the egg, which differs 

 essentially from the sexual animal, as the first "nurse" form A. 

 This gives rise to the two heteromorphous forms (lateral buds L, and 

 median buds M) ; of these, the median buds, in their capacity of 

 second " nurse " generation, produce the sexual generation G. The 

 abortive buds yielded by the ventral stolon represent a lateral branch 

 of the cycle of generations (A"). These two opposite views may be 

 tabulated as follows : — 



Alternation of Generations in Doliolum. 



GROBBEN's view : Uljanin's view : 



A (first "nurse" form) A ("nurse" form) 



L + M (second "nurse form) L + M + G (sexual generation) 



I 



G (sexual individual) 



We see from the above that if Uljanin's view is confirmed, the 



alternation of generations in Doliolum closel}' resembles that in the 



