W. K. BROOKS ON THE GENUS SALPA. 255 



In his second paper he says that the Faltenhulle, or, as I have called 

 it, the embryo sac, is lacking in Salpa democratica ; but the figures in 

 his first paper, especially Taf. XIV, Fig. 18, seem to indicate that this 

 structure is actually represented by a slight fold, as I have shown it to 

 be in Salpa hexagona, Plate XLV, Fig. 3. Whether it be totally absent or 

 very fully developed, no complication is thus introduced, for even in the 

 species where it is most developed, like Salpa pinnata and Salpa fusi- 

 formis, it takes no part in the formation of the embryo, and its presence 

 or absence is a matter of minor moment. We may therefore state with 

 confidence that, so far as the foetal membranes are concerned, the 

 various species of salpa (with the possible exception of Salpa scutigera, 

 which I have not studied) are fundamentally alike, although each 

 species has its own distinctive peculiarities, which often attain to such 

 prominence as to be noteworthy. 



Todarro's account of the foetal membranes is very different from 

 Salensky's or Barrois'; but, as Salensky has clearly shown, he has been 

 misled by a purely fanciful resemblance between the salpa embryo and 

 that of a mammal. His description has been so fully discussed by 

 Salensky that nothing more on the subject seems to be called for. 



As regards the fate of the embryo sac, my paper is simply a verifi- 

 cation of the studies of Barrois and Salensky, but Barrois says little 

 about the fate of the supporting ring and epithelial capsule, and while 

 Salensky's history of the epithelial capsule (Ectodermkeim of salpa in 

 general ; outer lamella of brood chamber in Salpa democratica) is very 

 explicit, it disagrees totally with my observations. 



Barrois finds (4), page 478, as I do, that the epithelial capsule is 

 thrown off, but his account of the minute details of the process in Salpa 

 af ricana is somewhat different from my observations on Salpa pinnata 

 and Salpa hexagona. He says, "The complete closure of the uterus 

 (embryo sac) is the signal for a great and important change, which 

 consists in the destruction of the cavity which has up to this time played 

 the part of a cavity of incubation, the cavity of the follicle." "The 

 membrane s (the epithelial capsule) which has up to this time been 

 united to the area where the placental membrane (supporting ring) and 

 the lower part of the wall of the follicle (roof of the placenta) are joined 

 together, now loses its connection at this point and is thrown off, leaving 

 the tissues of the embryo free in the interior of the uterus " (embryo sac). 



He describes and figures it as thrown off in a large sheet, but this is 

 certainly not the case in the species which I have studied. Some of my 



