376 WILSON. PVOESCDxS 
of the larva. In Esperella fibrexilis I have found the process, 
interpreted so differently, to take place in the opposite direc- 
tion. 
Marginal Membrane. — 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 
(Pls. 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 (axfe, pp. 303 and 335, and especially Pls. 
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 lke 
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 
