DEVELOPMENT OF THE GENERATIVE ORGANS. 719 



the structure of the parovarium is identical with that of the 

 germogen in the solid-bodied worms. 



In a more mature condition some of the epithelial cells con- 

 tain two nuclei (Fig. 94, C). Others contain one, or even two 

 included germ-ova ; the epithelial cells which contain germ-ova 

 also contain nuclei which exhibit a dividing nucleolus some of 

 these have one and others as many as four nucleoli. 



The deductions I draw from the appearances presented are : 

 (i) that the cells of the germogen are undergoing active multi- 

 plication, and that the nuclei divide and subdivide with or 

 without the subsequent division of the mother-cell. 



(2) That some of the nuclei assume the form of germinal 

 vesicles, whilst others undergo still further divisions, and ulti- 

 mately degenerate. 



(3) That the protoplasm of the germ ovum becomes definitely 

 separated around the germinal vesicle from the protoplasm of 

 the mother-cell by the formation of a distinct membrane, the 

 zona radiata. 



Similarity of the Processes of Germ and Sperm Formation. 

 It appears, therefore, that there is a strong resemblance be- 

 tween the manner in which the sperm-cells and germ-cells are 

 developed. In both the reproductive elements are developed 

 by endogenous cell-formation, and in both a part of the original 

 cell and its nucleus remain surrounding the reproductive 

 elements. The germ-ova are, however, much larger than the 

 spermatozoa, so that fewer are formed from each cell, and the 

 division of the mother-cells in the parovarium is far less 

 active than the division of the spermatospores in the testicle ; 

 so that in the second generation, whilst the polyblasts of the 

 testicle have numerous minute nuclei, the daughter-cells of the 

 parovarium have, at most, two or three, one of which, or at 

 most two, by subsequent division form a germinal vesicle and 

 an apparently inert or degenerating nucleus. 



Hertwig [368] has recently described similar relations be- 

 tween the development of germ -ova and spermatozoa in 

 Ascaris. He says : ' The formation of the ova and the sper- 

 matozoa are similar processes, and the knowledge of the one 



47 



