374 WILSON. (Vou. IX. 
In a little paper (35) embodying the main results of the 
present one, I endeavored to ascertain in terms of Weis- 
mannism the precise nature of the cells which combine to 
form the sponge gemmule, and arrived at the conclusion ‘that 
the gemmule cell, according to this view (Weismann’s) must 
be regarded as a true germ cell, in which all the germ plasm 
remains undifferentiated, vzz. in which none of it is transformed 
into ovogenetic plasm. Further, the gemmule cell pursues the 
parthenogenetic course of development —it keeps all its germ 
plasm” (p. 579). But at bottom it does not seem to me that 
a case of this kind, in which there is essential similarity 
between the products of a developing bud and a developing 
egg, tends to strengthen Weismann’s fundamental proposition 
that germ cells and somatic cells are radically different. 
Appendix.—I am fortunately able, some months after the 
completion of the present paper, to notice the remarkable 
memoir on the development of sponges, which M. Yves Delage 
has recently published.! In this memoir Delage describes in 
detail the post-larval development of Spongilla, Reniera, Aply- 
silla, and Esperella sordida. The essential features of develop- 
ment were found to be the same in all. I will briefly review 
his account of the Esperella development, and will then com- 
ment on certain points in which the account agrees or differs 
with mine. 
In the ciliated larva Delage distinguishes four classes of 
cells each of which is destined to form a particular part of the 
adult body. There is a covering layer of ciliated cells, wanting 
at the posterior pole. Scattered about between the basal 
portions of these cells is a discontinuous layer of cells called 
by the author efzdermic. At the posterior pole these lie at 
the surface, forming a nearly complete layer (in similar larva of 
Reniera they form, according to Delage, a complete layer). The 
remaining inner mass is composed of amoeboid and znxtermediary 
cells, the latter immobile and of a rather negative character. 
The ciliated cells absorb their flagella and migrate into the 
interior, ultimately becoming the lining cells of the flagellated 
1 Embryogénie des Eponges. Archives de Zoologie Expérimentale et Géné- 
rale. Année 1892. No. 3. 
