212 University of California Publications in Zoology. [VOL. 4 



of the second and third body cavities as will be seen from the 

 following (p. 70) : "The collar cavities are said to arise by a 

 pair of lateral evaginations from the archenteron. For the 

 present I accept this account of the origin of the second pair only 

 tentatively. The evidence furnished by Bateson does not seem 

 to me conclusive for accepting his statement. I think the phe- 

 nomena could be explained by a process of delamination or 

 migration, and a subsequent opening (or perhaps the small open- 

 ings are artifacts) . ' ' 



If one may judge from his descriptions and figures, Bateson 

 relied in his studies mainly upon transverse sections, whereas 

 the relation of the cavities to one another may be more certainly 

 followed on horizontal longitudinal sections. But these sugges- 

 tions hardly suffice to harmonize our observations. The other 

 alternative is that B. kowalevskii and D. pusillus, though so much 

 alike in most respects, differ widely in the origin and development 

 of their middle and posterior body cavities. But this is hardly 

 probable. 



Gland cells. One characteristic of the Enteropneusta is the 

 presence of numerous unicellular glands in the epidermis. Allu- 

 sion has already been made to the very active secretion of these 

 glands which occurs in period III. I have also called attention 

 to certain large round cells which make their appearance on the 

 periphery of the blastula. 



Those that happen to be on the endodermal portion of the 

 blastula are invaginated during gastrulation. They persist a 

 while in the endoderm, but I was unable to determine their sub- 

 sequent fate. 



The cells which are in the ectoderm increase in number 

 throughout the subsequent stages. During the latter part of 

 period I some of these are made deep blue by Mallory stain, indi- 

 cating the mucous character of their contents. 



In period II they become numerous in the collar region, and 

 at the two extremities. Some are empty; others are full of 

 secretion. 



In the early part of period" III the number in the collar region 

 is so great as to form an almost continuous layer. Here, in 

 Mallory-stained sections, the collar presents a deep blue border, 



