230 JOHNS HOPKINS UNIVEESITY MORPHOLOGICAL MONOGRAPHS. 



I have shown (p. 225) that the genital mass is present in the embryo 

 of Salpa pinnata before the stolon is formed, and that it gives rise to 

 nothing except the reproductive organs, and Salensky (17, pp. 50-57) has 

 recently shown that this is true of pyrosoma also. 



Seeliger, in his paper on the budding of salpa, gives the first correct 

 account of the origin of the testis, and shows that this, as well as the 

 follicle, is derived from the genital rod. 



In a paper published soon after, in 1888, on the origin of the alterna- 

 tion of generations of salpa (13), he says, p. 403: "Brooks bases the 

 female nature of the solitary salpa on the occasional occurrence of a 

 few cells which are distinguishable as eggs in the mesoderm when it 

 migrates into the cavity of the stolon." 



I have shown, however, p. 223, that not only a few but all the eggs 

 arise in the germinal mass at the root of the stolon, and that this is 

 the only place where new eggs are formed, either in the young stolon or 

 in the old one. 



Seeliger goes on to say that " I cannot regard Brooks' conclusion as 

 a necessary one, for the eggs of the chain-salpae are by no means defini- 

 tively perfect in the embryo, since they continue to undergo modifica- 

 tions until just before fertilization, like the mother cells of the testis and 

 the somatic cells in the mesoderm of the stolon. As we must regard the 

 testis, for example, or the branchial sac, as organs of the chain-salpas, 

 whether they arise from later generations of mesoderm cells, or are 

 derived from a definite part of the embryo ; so also must we regard the 

 ovary as an organ of the chain-salpa, since its modification from the 

 embryonic string of cells is only quantitatively different from the modifi- 

 cations which the testis and the branchial sac undergo." 



" Since, however, the testis of the chain form arises from the same 

 rudiment as the ovary, it is only speculation to regard the one as 

 belonging to the chain form, and the other to the solitary form, for the 

 same point of ' view would compel us to regard the solitary form as 

 hermaphrodite and the chain form as sexless." 



If it were true that the modifications of the ovary are only quantita- 

 tively different from those which are undergone by the rudiments of the 

 testis and the other organs of the chain-salpa, this objection would be 

 conclusive, but there is a most significant difference. In the young 

 stolon the rudiments of the testes and branchial sacs grow by cell multi- 

 plication, but after an egg cell is formed in the germinal mass it com- 

 pletely loses its vegetative power, and remains, until fertilization, a 

 single definite distinct ovum, as I have shown on page 222. 



