374 WILSON. [Vol. 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, viz. 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 epidermic. 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 intermediary 

 cells, the latter immobile and of a rather negative character. 



The ciliated cells absorb their fiagella and migrate into the 

 interior, ultimately becoming the lining cells of the flagellated 



1 Embryogenie des Eponges. Archives de Zoologie Experimentale et Gene- 

 rale. Annee 1S92. No. 3. 



