DESCRIPTION OF EPHYDATIA BLEMBINOIA. 99 



covery lies in the fact that the reproductive part of the 

 gemmnle and its protective coat are respectively formed from 

 classes of cells which are absolutely different, a conclusion 

 which is endorsed in the present paper, though the existence 

 of Marshall's "delicate membrane" round the central mass is 

 here denied. 



Wierzejski, evidently, has observed some phenomena which 

 he did not understand. According to this author a first heap 

 of naked amoeboid cells becomes differentiated to a central 

 mass of yolk containing cells, and a peripheral layer of 

 columnar cells. But he also states that the cells of the 

 mother sponge can even migrate to the body of the gemmule, 

 and thus increase its size. In the light of the facts which 

 have been described in the foregoing section of this paper, it 

 seems certain that Wierzejski discovered the migration of 

 cells, on the one hand, to form the columnar layer, and on the 

 other hand to feed the mother-cells of the reproductive cells 

 of the gemmule. Wierzejski in describing the first group of 

 cells uses the term " pseudomorula," and, probably knowing 

 that a true morula always becomes differentiated to two 

 classes of cells, he comes to the conclusion, as it appears, that 

 his " pseudomorula " must do the same. Consequently he 

 commits the mistake of describing the columnar layer of cells 

 as originating by differentiation from his pseudomorula 

 instead of by further migration from the sponge tissue. Not 

 only this, he was also unfortunate in not being able to discover 

 the true nature of the cells which migrated to the interior of 

 the gemmule, as he says, to increase its size. His failure was 

 probably due to the method of preservation he used. 



Before proceeding any further, it is necessary to refer to 

 Fiedler's account of the cells which he found during his in- 

 vestigations of Ephydatia fluviatilis (9). Fiedler de- 

 scribes and figures two kinds of cells (9, pi. xi, figs. 3 and 4, 

 and pi. xii, figs. 36 and 37). One kind, which he terms 

 "amoeboid Fresszellen," has granules of equal size in its 

 protoplasm, and a nucleus the chromatin of which is arranged 

 in a network. The other kind, which he terms " amoeboid 



