DESCRIPTION OF THE SEXUAL PRODUCTS. 



21 



Why are the male sexual cells so small and thread-like, and so 

 differently constituted from the eggs ? 



The dissimilarity between the male and the female sexual cells is 

 explained by the fact that a division of labor has arisen between the 

 two, inasmuch as they have adapted themselves to different missions. 



Fig. 10 A and B. Initial stages of the metamorphosis 

 of the seminal cell into the seminal filament, 

 after HERMANN. 



A, Seminal cell with pear-shaped nucleus ; B, seminal 

 cell with cone-shaped nucleus ; sz, seminal cell ; k, 

 nucleus with chromatin network, and uucleoli (n) ; 

 mst, body out of which the middle piece is developed ; 

 r, ring-like structure, which is in contact with the 

 middle piece, and is claimed to have relation to the 

 formation of the spiral membrane of the filament ; 

 /, caudal appendage of the seminal filament. 



Fig. 11 A and B . Two terminal 

 stages in the metamorphosis 

 of the seminal cell into 

 the seminal filament, after 

 FLEMMING. 



k, Nucleus, which has become 

 elongated to form the head 

 of the spermatozoon ; mst, 

 its middle piece ; /, its 

 caudal filament. 



The female cell has assumed the function of supplying the substances 

 which are necessary for that nutrition and growth of the cell proto- 

 plasm which a rapid accomplishment of the process of development 

 demands. It has therefore, while in the ovary, stored up in itself 

 yolk-substance, reserve material, for the future ; and consequently 

 has become large and incapable of motion. But inasmuch as it 

 is necessary for the accomplishment of a process of development 

 that union with a second cell from another individual should take 

 place, and since non-motile bodies cannot unite, therefore the male 

 element has been suitably modified to meet this second requirement. 



