392 



COMPAEATIVE ANATOMY. 



position, varying in different cases, within a cavity generally in the 

 neighbourhood of the intestine. In its relation to the formation of 

 buds the stolon of the Salpse also behaves differently from that of 

 Doliolum. In the latter, bud-generations sprout from the stolon ; 

 they are arranged in rows, are often dimorphic, and remain attached 

 to the stolon by short processes. In the Salpte similar buds arise by 

 outgrowth from the stolon, but each bud encloses within its base half 

 of the whole area of the stolon ; so that when two rows of such buds 

 are formed the material of the stolon itself is transferred to the body 

 of the buds. The maturity of the chain-like connected series of 

 young secondary buds (into which the primary bud divides) results, 

 in consequence of this disposition, in a separation (Fig. 206, n) from 

 the parent of the portion of the stolon concerned in its production. 



Fig. 206. Asexual form of Salpa 



pinnata (solitary fomi). n Eni- 



bryo-chain escaping to the ex- 



tei'ior. 



Fig. 207. Sexual form of Salpa pinnata 

 (chain form), t Connecting bar. a Incurrent 

 orifice. b Excurrent orifice. c Ganglion. 

 d Gills. / Heart, h Ventral groove, r Hepatic 

 pouch. vim Embryo with embryonic organs 

 (both figures after C. Vogt). 



This arrangement brings about an " alternation of generations," 

 seeing that the forms provided with a stolon are always permanently 

 devoid of sexual organs. On comparing this series of pheenomena 

 with that occurring in the Ascidiee, we find, just as in the Ascidiae, 

 proliferous outgrowths, namely, the stolons. The outgrowth in 

 question is here confined to a definite part of the body. In Pyro- 

 soma a proliferous stolon is present, sunk in the mantle, and from 

 every such stolon only a single bud is developed; side by side with 

 this are developed sexual organs. Accordingly it is not possible to 

 suggest that the stolon belongs to the sexual apparatus. In the 

 Salpas and in Doliolum, contra,ry to what we find in Pyrosoma, the 

 proliferous stolons give rise to copious generations of buds. In this 

 case, however, the absence of a sexual apparatus is the accompaui- 



