280 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



embryo and ultimately from the egg, and not from the lateral walls of 

 the placenta, which, as Barrois points out, are derived from the walls 

 of the cul-de-sac, and are formed from the body of the chain-salpa. 



He says that degeneration begins around the circumference of the 

 membrane which forms the roof of the maternal chamber and the floor 

 of the foetal chamber, and that it takes place in such a way that this is 

 set free from the inner surface of the wall of the placenta. The degen- 

 eration extends towards and finally reaches the central thickening, or 

 " bell-clapper," which loses its distinct epithelial character and becomes 

 an irregular mass of cells. At the same time there is an increase in the 

 products of degeneration, which are formed from two sources: 1st, at 

 the expense of the two great masses of elongated cells which form the 

 wall of the placenta at the level of the superior portion of the foetal 

 chamber, and 2d, at the expense of the central portion of the folded 

 membrane, at the middle of which there is heaped up above the "bell- 

 clapper" a great accumulation of granules and protoplasm. The out- 

 lines between the cells in the degenerating area disappear, and for a 

 time the nuclei can be seen scattered through the transparent mass 

 which is produced by their fusion, but as degeneration goes on the 

 whole becomes granular, with nuclei and oviform bodies. 



The "roof of the foetal chamber" of Barrois seems, from his figures 

 and description, to be what I have called the roof of the placenta and 

 have marked 10 in my figures ; and the " folded membrane " which he 

 regards as the floor of the foetal chamber and the roof of the maternal 

 chamber is the horizontal fold, which is shown just above the "bell- 

 clapper," 24, in my Plate XVIII, Fig. 4, although serial sections would 

 have taught him that it runs through only a few sections, and does not 

 form a partition, since there is a free channel both in front of it, Fig. 3, 

 and behind it, Fig. 5. His " oviform bodies " are the big migrating cells, 

 29, and his "great accumulation of degenerating cells and nuclei and 

 granular protoplasm" is the spongy mass of strings of follicle cells 

 which fills the upper part of the placenta. 



Salensky's account of the placenta (5) is scattered through his 

 pages in such a way that it is hard to follow. The placenta of Salpa 

 pinnata is treated on pp. 102, 111, 123 and 384; that of Salpa africana, 

 on pp. 155 and 157 ; that of Salpa punctata, on pp. 331, 332 and 344; that 

 of Salpa runcinata (fusiform), on pp. 347, 349 and 350; that of Salpa 

 bicaudata, on pp. 368 and 397, and that of Salpa democratica, on pp. 379, 

 380 and 384. 



