I02 JOURNAL OF THE 



If for convenience's sake we adopt the point of view of 

 Weismann, and regard the Qgg cell as characterized by the 

 possession of a "germ plasm," the gemmule cells too (un- 

 less the resemblances between the gemmule and egg embryo 

 are accidental) have some claim to the possession of this 

 plasm. By making a little further use of Weismann's the- 

 ory, the nature of the gemmule cell [t. ^., a mesoderm cell, 

 which, together with others, forms a gemmule) may per- 

 haps be stated with some precision. Of the two polar 

 bodies found in non-parthenogenetic eggs, Weismann 

 believes that the first carries oif ovogenetic plasm, the 

 second carries off one-half the germ plasm. In the case of 

 the sponge gemmule, a mesoderm cell does not itself 

 become differentiated into an ovum, but the necessary 

 amount of nutriment for the embryo is got by the associa- 

 tion of numerous such cells. Hence there is in the gem- 

 mule cell no special histogenetic (ovogenetic) plasm, and 

 consequently no first polar body. There is, of course, no 

 fertilization, therefore no second polar body. The gemmule 

 cell, according to this view, must be regarded as a true 

 germ cell, in which all the germ plasm remains undiffer- 

 entiated, viz., in which none of it is transformed into ovo- 

 genetic plasm. Further, the gemmule cell pursues the 

 parthenogenetic course of development — it keeps all its 

 germ plasm. 



Gemmules apparently develop anywhere in the sponge 

 mesenchyme. It must, therefore, be assumed that any 

 mesenchyme cell may become a gemmule cell, and conse- 

 quently that it contains germ plasm. The same conclu- 

 sion is reached by the study of the egg development, for 

 it seems that any mesenchyme cell may develop into an 



The gemmule development in Tedania pursues much 

 the same course as in Esperella. The early stages in the 

 formation of the gemmule, owing to the extremely small 



