400 Mr. H. J. Carter un the 



Comparison of the Development of the Sponge developed from 

 the embryo of Halichondria simulans loitJi that of Spongilla 

 developed fi-om the seed-like body. 



On comparing the development of tlie sponge from the 

 embryo of Halichondria simulans after it has become stationary 

 or fixed (viz. the Fomlh Period) with that developed from the 

 seed-like body of Spongilla^ one cannot help being struck with 

 the facts that the appearance of the latter at first in an opaque 

 uuciliated mass, as it issues from the hiliform opening of the 

 seed-like body, followed by the extension of a homogeneous- 

 looking sarcode, denticulated at the margin like the pseudopodia 

 of an Ama-ba^ then the projection from this substance of 

 spicules which thus raise and angulate the previously round 

 surface, afterwards the shrinking inwards of the opaque or 

 parenchymatous portion while the dermal layer is still left 

 upon the points of the spicules in the form of the " investing 

 membrane " and its '' cavity " (the intermarginal cavity of 

 Bowerbank) beneath, together with the exit from the seed-like 

 body of its transparent spherical germiniferous cells entire and 

 their subsequent appearance in the general mass as ampuUa- 

 ceous sacs ('Annals,' 1849 & 1857 respectively, Zocc.ci'W.), are all 

 identical with what we have observed in the development of the 

 embryo of Halichondria sinmlans during the Fourth Period. 

 But here the identification ends, inasmuch as there are 

 no spicules already formed in the seed-like body as there are 

 in the embryo oi Halichondria simulans even before the latter 

 leaves the parent, while the contents of this body chiefly con- 

 sist of the transparent spherical cells, which already contain the 

 cell-germs of the spongozoa, preparatory to their passing into 

 the form of the ampullaceous sac the moment they get into the 

 general mass which grows out from the hiliform opening of the 

 seed-like body ; so that, in fact, while the spicules are already 

 developed at a very early period in the embryo of Halichondria 

 simulayis, and the groups of spongozoa, which finally form the 

 ampullaceous sacs, do not appear before the sponge is fully de- 

 veloped, the reverse is the case with the sponge-substance which 

 issues from the seed-like body of Spongilla, where at first there 

 are no spicules present, but the ampullaceous sacs are already 

 foreshadowed by the transparent spherical germiniferous cells, 

 each of which measures at this time l-800th inch in diameter. 

 Now it so happens that in the embryo of Halichondria simu- 

 lans there are many cells in the body-substance about l-3000th 

 inch in diameter, which, bemg evidently filled Avitli cellulse 

 (PL XXI. figs. 21, c, & 22, c), I have before suggested might be 

 the early forms of the ampullaceous sacs ; and if this be the 



