W. K. BROOKS ON THE GENUS SALPA. 253 



= Amniotic membrane, Todarro, for inner 



fold. 

 = Reflected portion of the uterus, Barrois 



for outer fold. 

 = The two folds together make the decidua 



reflessa of Todarro. 

 = Uterus, Barrois and Todarro, for the 



cavity of the embryo sac. 

 = Its aperture is the neck of the uterus, 



Todarro. 



= The space between the two folds, y', in 

 my figures, is the amniotic cavity of 

 Todarro. 



So far as the origin and anatomical relations of the foetal membranes 

 are concerned, the account which I have given is little more than a repe- 

 tition of the accounts which have already been published by Barrois (4) 

 and Salensky (5), and their descriptions show that while the various 

 species present slight differences of detail, especially as regards the degree 

 of development which is reached by the embryo sac, the history is essen- 

 tially the same in Salpa democratica, hexagona, africana, fusiformis, 

 pectinata, and pinnata, or in all the species which have been studied, 

 with the possible exception of Salpa scutigera (bicaudata). 



Salensky has shown that in each species the egg and the embryo 

 have certain distinctive specific characters which might be used for the 

 diagnosis of species, and the illustration and description of these specific 

 features form one of the most interesting sections of his memoir, but it 

 is to be regretted that he did not bring all these specific characteristics 

 together in one place, so that the rest of his paper might be devoted to 

 an account of the common characteristics of the salpa embryo. There 

 can be no doubt that the general effect of his paper is to convey to the 

 reader an exaggerated notion of the difference between the embryos of 

 the different species, and this effect is all the greater since the terms 

 which he uses in his description of Salpa democratica are quite different 

 from those by which he designates the same parts in other species. 



Careful examination of his first paper (2) will show, however, that so 

 far as the foetal membranes are concerned, the only difference between 

 Salpa democratica and all the other species (possibly with the exception 

 of Salpa scutigera) is the lack of the embryo sac, or, at least, its very 

 scanty development; but as the wall of the embryo sac in the other 



