DESCRIPTION OF THE SEXUAL PRODUCTS. 21 



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

 <litr'iviitly constituted from the e<rrs 'I 



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. 



Tig. 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 nucleoli () ; 

 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 ; 

 t caudal appendage of the seminal filament. 



Fig. HAandB. Two terminal 

 stages in the metamorphosis 

 of the seminal cell into 

 the seminal filament, after 

 FLEMMING. 



Tc, Nucleus, which has become 

 elongated to form the head 

 of the spermatozoon ; mst, 

 its middle piece ; f, 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. 



