100 RICHARD EVANS. 



Nahrzellen/' has granules of unequal size in its protoplasm, 

 and a nucleus with a distinct nucleolus. 



Zykoff, who writes in the light of Fiedler's discoveries, 

 considers the appearance of refractive yolk substance in a few 

 amoeboid cells of the mesenchyme as the first development of 

 the gemmule. He finds these cells belong to neither of 

 Fiedler's classes of cells, for they have the protoplasm of 

 the " amoeboid Fresszellen " and the nucleus of the "amoe- 

 boid Nahrzellen." These cells, together with others like 

 them, but without yolk substance, are described as creeping 

 together to form a spherical heap of cells, which differen- 

 tiates to a central mass which consists of yolk-cells, amongst 

 which here and there are scattered amoeboid cells of the 

 mesenchyme, and to a peripheral sheet of mesenchyme cells 

 without yolk, which pass to the general mesenchyme of the 

 sponge. Zykoff has described Wierzejski's figures as being 

 diagrammatic and far from the truth. His figures, however, 

 might with a certain amount of propriety be described in the 

 same terms, and Weltner's criticism that they are not natural 

 is quite true. Zykoif, however, is in error when he says the 

 cells of the peripheral sheet above mentioned do not contain 

 yolk. It is true that there are cells among them without 

 spherical bodies in them, the trophocytes of the present 

 paper; but it is equally true that the greater number of them 

 contain bodies which are in all respects similar to the "re- 

 fractive yolk substance " which Zykoff professes to have seen 

 " in a few amoeboid cells of the mesenchyme," which he de- 

 scribes as the appearance of the first development of the 

 gemmule. Zykoff has here failed to distinguish between two 

 classes of cells, and consequently the description he has given 

 of them is not true of either. The cells which he found to 

 contain yolk-bodies in the sponge tissue, and which, he 

 assumes, become the yolk-cells, develop, as it appears, to the 

 columnar cells, and do not fall under the category of " amoe- 

 boid Fresszellen," or that of " amoeboid Nahrzellen." They 

 form a separate class, while the other cells found among them 

 as well as among the yolk-cells must be placed in a class by 



