270 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



I shall show that, in every one of the regions, the follicle ultimately 

 becomes disintegrated, loses its identity as a distinct tissue, and breaks 

 up into wandering, amoeboid follicle cells, which make their way into all 

 parts of the embryo and gradually disappear. 



While it is, of course, impossible to trace in sections the individual 

 history of every one of these wandering cells, there is no evidence that 

 any of them become converted into any of the cells of the embryo, while 

 there is ample evidence that they are all used up as food, and that the 

 function of all parts of the follicle is nutritive. 



It will be best to treat each region of the follicle separately, and I 

 shall speak first of the dorsal or embryonic portion of the somatic layer ; 

 second, of the somatic lining of the atrium and gill tubes ; third, of the 

 portion of the visceral layer which penetrates between the blastomeres ; 

 fourth, of the portion of the visceral layer which invests the blastomeres ; 

 and fifth, of the placental portion of the somatic layer of the follicle. 



SECTION 4. The Disintegration of the Embryonic Portion of the Somatic 



Layer of the Follicle. 



I have shown, page 43, that the embryonic part of the somatic layer 

 of the follicle separates at an early stage, from the part which forms the 

 roof of the placenta, and that it soon afterwards breaks up into discon- 

 nected follicle cells, which separate from each other, and, becoming 

 amoeboid, wander into all parts of the body cavity of the embryo. 



This is the region where the history of the follicle is simplest and 

 easiest to follow, and where the evidence of its nutritive function is most 

 obvious, and both Barrois' and Salensky's observations are consistent 

 with my statement regarding it. Barrois, 473, says that this region of 

 the embryo of Salpa africana consists of two layers ; those which I have 

 called the epithelial capsule and the somatic layer of the follicle; and 

 that the latter soon disappears, although he was not able to satisfy 

 himself whether it is actually destroyed or is simply fused with the 

 inner layer. 



Salensky has observed the phenomenon in Salpa pinnata and Salpa 

 fusiformis (5), p. 130 and p. 352, and he has described it in words which 

 exactly express my own view, although he interprets the change as the 

 result of growth (Wucherung) of the follicle rather than its disinte- 

 gration. 



He says, p. 130, that in Salpa pinnata a most important and signifi- 



