272 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



SECTION 5. The Fate of the Follicular Lining of the Atrium and Gill Tubes. 



I have already fully described on page 29 the way in which the 

 atrium and gill-slits are formed by the invagination, from the somatic 

 layer of the follicle, of two tubes, which I regard as the follicular equiva- 

 lents of two perithoracic tubes. I have also shown, page 45, that the 

 follicular lining of the perithoracic structures ultimately breaks up into 

 amoeboid cells, which at first almost completely fill the atrium, although 

 they gradually disappear as development progresses. 



Salensky's account of the origin of these structures is very different 

 indeed from mine, since he believes, page 140, that the cloaca of salpa 

 is not a distinct chamber, but only a part of the pharynx; that the "gill" 

 is formed by the meeting and union of two outgrowths from the walls of 

 the pharynx ; and that the primitive digestive cavity consists at first of 

 two independent halves, separated from each other on the middle line. 



It is only necessary to compare his figures with my own, especially 

 his Plate XIV, Fig. 33, with my Plate XIV, in order to discover that he 

 has mistaken the two gill tubes, gf iv , of my figures, for the digestive 

 cavity, and that a complete series of sections would have shown him the 

 atrium g'", at a higher level, and the true pharynx c, at a lower level, at 

 the stage of his Fig. 33. 



His account of the origin and fate of the inner lining of his, so-called, 

 primitive digestive cavity is identical with my own, however, for he 

 says that it is derived from the somatic layer of the follicle (Follikel- 

 wand), and that it breaks up into amoeboid cells which are gradually 

 used up as food and disappear. 



He says, on page 131, that each of the separate halves of which the 

 primitive digestive cavity at first consists, is open above, where it is 

 fastened to the somatic layer (Follikelwand), and that through this 

 opening a string of follicle cells runs downwards into the digestive 

 cavity, to end in a mass of cells which, in part, form its inner lining and, 

 in part, lie free within it. He says, page 131 and page 127, that these 

 lining cells have no formative function, but that they are purely nutri- 

 tive, and that they gradually become less and less abundant as they are 

 converted into food. 



So far then there is no very great discrepancy between Salensky's 

 account of the fate of the follicle and my own. 



He regards the disintegration of the somatic layer as growth, but he 

 agrees with me that it does disintegrate, and he regards the gill-tubes as 



