404 ZOOLOGY. 



embryonic parts of the placenta arising, respectively, from 

 the wall of the ovarian sac and from certain lai-ge cells (blas- 

 tomeres) on the adjacent (lifemal) face of the embryo. Thus 

 the asexual development of the Salpa is like that of the germ- 

 masses destined tu form the Cercarice developed in the body 

 of the Redia of the Disfomaj and is also like that of the 

 jjlant lice (Huxley). This is a reaflSrmation and extension 

 of the original view of Chamisso. 



To recapitulate, the life-history of the Salpa is as follows : 

 There are two kinds of individuals : a. solitary, asexual : 5, 

 social, aggregated, and hermaphroditic. 



(1.) Tlie solitarv, asexual Salpa produces by budding a 

 chain of hermaphrodite Salpae ; the latter produce a fertil- 

 ized 



(2.) Egg, which passes through a — 



(3.) ^lorula and — ■ 



(4.) Gastrula stage, contained and growing in a placenta- 

 like organ, where the embryo is directly nourished by the 

 Talood of the parent, the emliryo finally becoming — 



(5.) A solitary asexual Salvia. 



We thus have a true alternation of generations, like the 

 sexless Hydroid and its sexual Medusa, the asexual AjiJiis 

 and its last brood of males aud females : the asexual Redia 

 and the sexual Didoma ; in all these cases the ofEspring (&) 

 of the asexual individual {a) is unlike the parent, but the off- 

 spring (f) of the second generation (J) is like (a) the grand- 

 parent. 



" In Doliolum the reproductive processes are much more 

 complicated, for not only do the sexually produced yonng 

 undergo a metamorphosis, but a new series of generations is 

 introduced into the life-histoiy. The eggs are laid, and the 

 larvge which issue from tliem are provided with tjiils and re- 

 semble Ascidian larva?. They develop into asexual forms, 

 which differ from the sexual forms, and are provided with a 

 dorsal stolon; the ventral stolon (stolon of Salpa) is rudimen- 

 tary. Two different kinds of buds are formed on this dorsal 

 stolon, viz., median buds and lateral buds. The lateral buds 

 have a slipper-like form, and are without the cloacal cavity; 

 they do not reproduce themselves, but are concerned wiA the 

 nourishment of the asexual form. The latter as it increases 



