No. 3-] DEVELOPMENT OF MARINE SPONGES. 377 



the amoeboids. In Esperella and the other sponges only a 

 portion are so absorbed, while the remainder throw out proc- 

 esses and unite with one another and the now multinucleate 

 amoeboids, to form a syncitial net-work. In the development 

 of a chamber several of the multinucleate masses approach 

 one another and form a continuous wall round a central space. 

 The space becomes the cavity of the chamber, round which 

 the nuclei of the absorbed ciliated cells arrange themselves in 

 a regular fashion, while the nucleus of the amoeboid sur- 

 rounded by protoplasm escapes from the periphery of the 

 chamber anlage, and becomes a wandering cell of the meso- 

 derm. The ciliated cells not associated with the amoeboids, 

 but which are merely part of the syncitium, unite in the same 

 manner and form chambers." 



The multinucleate formative cells I have described evidently 

 correspond to Delage's multinucleate amoeboids. But while 

 Delage agrees with Gotte and myself (35, and ante) in regard- 

 ing the smaller peripheral bodies as nuclei, he differs com- 

 pletely in his explanation of their origin — I regard them as 

 derived from the central larger nucleus of the cell. 



Delage's observation that chambers arise from the fusion of 

 several multinucleate groups, corroborates the account I have 

 given of one of the methods of chamber formation (35, and 

 ante, p. 312), though, as before said, we differ greatly in our 

 views of the ultimate origin of such groups. But on the other 

 hand I have repeatedly observed that chambers may also be 

 formed by formative (amoeboid) cells which group themselves 

 in hollow spheres. Some of these cells may contain but a 

 single nucleus, while others contain more. Observations such 

 as this would seem to disprove Delage's thesis that the col- 

 lared cells are the immigrated ciliated cells of the larva. 



Canal Epitltclium. — Delage, like myself, finds that the 

 canals arise independently of one another, as irregular spaces 

 in the inner mass, that they gradually become lined with a 

 definite epithelium and unite with one another and with the 

 chambers to form a connected system. Regarding the origin 

 of the canal epithelium, however, Delage entertains widely 

 different views from my own. His account is as follows : 



