376 WILSON. [Vol. IX. 



of the larva. In Esperella fibrexilis I have found the process, 

 interpreted so differently, to take place in the opposite direc- 

 tion. 



Marginal Membratic. — A marginal membrane, essentially 

 like the ectodermal membrane I have described surrounding 

 the young Esperella and Tedania, is formed in all the sponges 

 studied by Delage. The author's account of the manner in 

 which the membrane is formed differs, however, from mine. 

 In Spongilla and Esperella sordida Delage describes the mar- 

 ginal ectodermic cells of the just attached sponge as creeping 

 outwards in an amoeboid fashion and so forming a considerable 

 membrane, at the edge of which the cells remain amoeboid 

 (Pis. XIV, XV). As my figures show I have never found the 

 marginal ectodermic cells amoeboid. On the contrary I have 

 found the ectoderm (epidermis), as it extends out to form the 

 membrane in question, retaining a continuous edge, which 

 could not be the case if the individual cells of the margin 

 threw out processes {ante, pp. 303 and 335, and especially Pis. 

 XXI and XXII). The condition, at least the later condition, 

 of the membrane in Aplysilla, as described by Delage, accords 

 better with my observations than does his account of the 

 membrane in Spongilla and Esperella. In Aplysilla the mar- 

 ginal epidermic cells at first throw out amoeboid processes, 

 but later assume regular shapes, and arrange themselves along- 

 side one another in such a way as to give to the membrane an 

 even continuous edge. 



Flagellated Chambers. — Several of the stages in the forma- 

 tion of the chambers that M. Delage has found, are quite like 

 such as I have seen, but the whole process is construed very 

 differently. Delage's account is as follows: "The ciliated cells 

 after their migration into the interior are seized upon and 

 engulfed, amoeba-fashion, by the amoeboid cells. Complete 

 fusion takes place between the bodies of the absorbed cells 

 and that of the amoeboid, but the nuclei of the former remain 

 distinct and arrange themselves round the much larger nucleus 

 of the latter. In this way are formed the multinucleate cells 

 which have been interpreted so differently by previous ob- 

 servers. In Spongilla all the ciliated cells are absorbed by 



