DESCEIPTlOIs OF EPHYDATIA BLEWBINfilA. 101 



themselves. In the present account they have been termed 

 " trophocytes/^ and seem to be identical with Fiedler's 

 " Nahrzellen." Zykoff found the cells in question among the 

 yolk-cells, but does not properly account for their absence 

 from that position in later stages. It seems certain that 

 Zykoff never saw the first stages in the development of the 

 gemmule. His first figure has not the remotest resemblance 

 to the first rudiment of the gemmule. If he never saw the 

 first stages, this explains how he missed the cells with nuclei 

 the chromatin of which is arranged in a network at first, but 

 later on presents the appearance of a modified vesicular 

 nucleus. However, there seems to be little doubt but that 

 these cells form a different class from the above-mentioned 

 classes, and correspond when they are coming together in all 

 respects to Fiedler's " Fresszellen." Consequently, at the 

 time the peripheral layer of cells appears the w^liole group 

 consists of three classes of cells : first, the mother-cells of the 

 yolk-cells ; secondly, the mother-cells of the columnar cells ; 

 and thirdly, the " trophocytes." The first class consists of 

 Fiedler's "amoeboid Fresszellen," the third class of his 

 "amoeboid Nahrzellen," while the second class consists of 

 those cells which, according to Weltner, belong to neither of 

 Fiedler's classes, and, according to Zykoff, occupy a position 

 between the two. 



Now that the somewhat diflticult questions of the origin and 

 fate of the cells above discussed seems to have been solved, 

 there remain but few points to be considered in connection 

 with the formation of the protective coat of the gemmule. 



At no stage 'in the formation of the gemmule was a delicate 

 coat or membrane, situated internally to the inner chitinous 

 layer, found to exist. It often happens, however, that the 

 outer limit of the reproductive portion of the gemmule is 

 sharp, smooth, and well defined. But there is no membrane, 

 the sharpness of contour being merely the result of the pres- 

 sure exerted by the mass of cells on the inner chitinous layer. 



The cells of the outer layer are columnar in form, and not 

 club-shaped. This, however, is a small point hardly worthy 



