282 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



derived from the follicle, and that the side walls and part of the roof 

 are formed from the lower part of the epithelial capsule or " Ectoderm- 

 keim," which becomes thickened, and, losing its connection with the 

 part which invests the embryo, bends inwards towards the axis of the 

 placenta. 



He says, p. 157, that while the roof of the placenta of Salpa africana 

 is formed from follicle cells, and not, as Barrois states, from blastomeres, 

 his own studies of this species completely confirm all of Barrois' chief 

 results. 



I have shown, however, that Barrois has mistaken a transverse rod 

 for a complete horizontal diaphragm; and that the division which he 

 describes, into a foetal chamber and a maternal chamber, is the result of 

 this error, and that his figures show that there is really only one chamber 

 in this species. 



Salensky says, pp. 347, 349 and 350, that the placenta of Salpa run- 

 cinata (fusiformis) is very similar in its changes of form to that of Salpa 

 africana, although it arises in a different way. It is at first cup-shaped, 

 but it soon divides into two parts, an upper one which forms part of the 

 body of the embryo at the. time of its escape, which he calls the f ratal 

 placenta, and a lower one which remains in the body of the chain-salpa, 

 and which he calls the maternal placenta. 



The study of his figures will show, however, that there is no division 

 into two chambers, and that the only reason for calling the upper part 

 a foetal placenta is, that it is carried off by the embryo to be used up as 

 food after its escape. His figures of Salpa runcinata and Salpa demo- 

 cratica show only one chamber, in direct connection with the blood 

 system of the chain-salpa, and while, in the absence of any figures of 

 transverse sections, his longitudinal sections of the placenta of Salpa 

 bicaudata are almost unintelligible, they do not indicate any difference 

 from the other species in this particular. 



I think that we may affirm, then, that no species of salpa has been 

 proved to have a fcetal placenta, and that all the evidence indicates that 

 it is in all cases a single chamber, in communication with the blood 

 system of the chain-salpa. 



SECTION 9. The " Test Cells " of Salpa. 



I have shown, page 220, that the follicle cells of salpa must be 

 regarded as germ cells which have become differentiated from the 



