404 ZOOLOGY. 
embryonic parts of the placenta arising, respectively, from 
the wall of the ovarian sac and from certain large cells (blas- 
tomeres) on the adjacent (hemal) face of the embryo. Thus 
the asexual development of the Salpa is like that of the germ- 
masses destined to form the Cercarie developed in the body 
of the Redia of the Distoma ; and is also like that of the 
plant lice (Huxley). This is a reaffirmation 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 ; b, 
social, aggregated, and hermaphroditic. 
(1.) The solitary, asexual Salpa produces by budding a. 
chain of hermaphrodite Salpe ; the latter produce a fertil- 
ized 
(2.) Egg, which passes through a— 
(3.) Morula and— 
(4.) Gastrula stage, contained and growing in a placenta- . 
like organ, where the embryo is directly nourished by the 
blood of the parent, the embryo finally becoming— 
(5.) A solitary asexual Salpa. 
We thus have a true alternation of generations, like the 
sexless Hydroid and its sexual Medusa, the asexual Aphis 
and its last brood of males and females; the asexual Redia 
and the sexual Distoma ; in all these cases the offspring (2) 
of the asexual individual (a) is unlike the parent, but the off- 
spring (c) of the second generation (0) is like (a) the grand- 
parent. 
‘In Doliolum the reproductive processes are much more 
complicated, for not only do the sexually produced young 
undergo a metamorphosis, but a new series of generations is 
introduced into the life-history. The eggs are laid, and the 
larvee which issue from them are provided with tails and re- 
semble Ascidian larve. 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 with the 
nourishment of the asexual form. The latter as it increases 
