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 : 
(1) 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 [868] 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 
