MUSEUM OF COMPARATIVE ZOOLOGY. 337 



Summary and General Conclusions. 



The life history of Salpa may be stated briefly, as follows : 



The solitary Salpa — female — produces a chain of males by bud- 

 ding, and discharges an egg into the body of each of these before 

 birth. 



These eggs are impregnated while the zooids of the chain are very 

 small, and sexually immature, and develop into females, which give 

 rise to other males in the same way. 



Since both forms are the offspring of the female, the one by bud- 

 ding, and the other by true sexual reproduction, we have not an 

 instance of " alternation of generations," but a very remarkable 

 difference in the form and mode of origin of the two sexes. 



After the fetus has been discharged from the body of the male the 

 latter grows up, becomes sexually mature, and discharges its sper- 

 matic fluid into the water, to, fertilize the eggs carried by other imma- 

 ture chains. 



The fact that impregnation takes place, not, as we should expect, 

 within the body of the solitary, but within that of the chain-salpa is 

 no valid objection to the view that the latter is simply a male, for the 

 number of animals whose eggs undergo impregnation within the body of 

 the female is quite small, and in at least one genus, " Hippocampus," 

 the unfertilized ova are received into a specialized brood-sac upon the 

 body of the male, and there impregnated. 



We can also find an analogy for the singular fact that the eggs of 

 Salpa always develop females, while the males originate by budding. 

 The fertilized eggs of the bee always develop female embryos, while 

 the virgin bee, or one from the body of which the spermathecse have 

 been removed, produces only males, and Professor McCrady has pointed 

 out that the production of the male bees in this manner can be best 

 interpreted as a process of ovarian gemmation. The reproductive 

 process of the bee accordingly presents a very striking parallel to that 

 of Salpa. We cannot fail to associate the fact that in these two ani- 



Tunicata. Huxley pointed out, in 1860 (Anatomy and Development of Pyrosoma, p. 

 212), that each bud carries away part of the ovary of its parent, and one fully devel- 

 oped ovum ; and he says : " It is not a little remarkable that the first recognizable part 

 of the new organism should be the foundation of that structure which will eventually 

 develop into a creature distinct from it." Other observers have described a precisely 

 similar occurrence in other Tunicata. 



