MUSEUM OF COMPARATIVE ZOOLOGY. 347 



culates within, not around tliern, proves that their cavities are continuations, not of the 

 cloacal, or, as I have termed it after Huxley, the atrial cavity, but of the sinus system 

 or body cavity of the parent. Instead of one ovarian rod, I found two, and failed to 

 discover that they are hollow. In this paper Kowalevsky says that this tube gives rise 

 to the ovaries of the chain-salpae, although in his paper on Pyrosoma, published in 1S75, 

 and already quoted, he seems to agree with me in holding that they develop eggs before 

 the chain-salpa: are formed, and discharge a single egg into each one of these. He 

 fails to see, however, that this proves the solitary salpa to be the true female. His 

 fifth or nerve tube I did not find. 



I was unable to homologize the placenta of Salpa with any organ of any other Ascid- 

 ian. Leuckart compares the foot of a Lamellibranch, the tail of Appendicularia, and 

 the placenta ; but this comparison seems to be rather fanciful. Kowalevsky suggests 

 that the placenta may be the homologue of the cyathozooid of Pyrosoma, and the first 

 generation of Doliolum. He says (p. 414) : " At the close of this communication I may 

 be permitted to call attention to the general analogy which is to be remarked between 

 the development of Salpa, Pyrosoma, and Doliolum. In Salpa the egg forms an em- 

 bryo which divides into two parts ; one forms the placenta, and the other the embryo 

 proper, which bears a dorsal [haemal] stolon from which the sexual individuals bud. 

 The egg of Pyrosoma forms a very rudimentary embryo, which produces, through 

 budding, four embryos, which now, in turn, develop four sexual individuals from a 

 dorsal stolon. The egg of Doliolum forms a perfect but sexless individual, which puts 

 forth a ventral stolon, from which are formed individuals with a dorsal stolon, out of 

 which the sexual individuals bud. From this comparison it is manifest that, between 

 the placenta of Salpa, the rudimentary embryo of Pyrosoma, and the free-swimming 

 stolon-bearing Doliolum an analogy exists ; that, in a word, we here have before our 

 eyes the different steps in the same developmental process." 



I think there can be no doubt that Salpa has originated in a manner somewhat simi- 

 lar to that here pointed out ; although the fact that the solitary form or egg-embryo is 

 not sexless, but a female, would seem to indicate that the relation between the three 

 genera cannot be exactly as it is here described. In my account of the manner in 

 which the evolution of Salpa may be supposed to have taken place, I purposely refrained 

 from referring to Doliolum, as we know so little of its development. A complete his- 

 tory, by one observer, of all the stages of one species of this genus, from the egg 

 through all the alternations around to the egg, would be of the greatest interest. At 

 present our knowledge is made up of fragments by various observers of isolated 

 stages in the development of various species. 



The Memoir by Todarro now remains to be noticed. This is an elaborately illustrated 

 quarto of 150 pages ; and the observations recorded, as well as the conclusions 

 reached, are so utterly at variance with all that has been done by previous observers 

 that it seems impossible to reconcile them. According to this writer, Salpa is the syn- 

 thetic type of all the Vertebrata, and presents, during its development, peculiarities 

 which are characteristic of each of the classes of this group, including the Mammalia. 

 It is an allantoi'dian vertebrate, developed in a true uterus, which is composed of a mus- 

 cular, a vascular, and a mucous layer ; and after impregnation the neck of the uterus 

 becomes closed by a plug of mucus, and the embryo forms an allantois, exactly as in 

 the higher Vertebrata. The sections which are represented in the figures are so strik- 

 ingly like those of the earlier stages of the higher vertebrates that T am unable to make 

 any comparison between them and my own observations The work seems to have been 



