REPRODUCTION. 



847 



material constituting their structure a rearrangement takes place, 

 and gradually each of these daughter-cells becomes transformed into 

 a spermatozoon, with its characteristic parts : the head, middle piece, 

 and tail. It is evident, therefore, that each spermatogenic cell gives 

 rise to four spermatozoa, all equally qualified to take part in the 

 physiological process assigned to them fertilization. This is dia- 

 gramatically represented in the figure of Boveri (Fig. 382). 



In the ovary we find the Graafian follicle, containing two dif- 

 ferent kinds of cells: one large one, the ovarian ovum, correspond- 

 ing to the spermatogenic cell of the testicle; and more numerous 

 smaller ones, supporting or protecting the larger by forming a cap- 

 sule, as it were, around it and constituting the membrana granulosa 



Fig. 384. Schema to Indicate Process of Maturation of Ovum. 

 ( BOVERI. ) ( HOWELL. ) 



1, Ovarian egg. 2, First polar body. 3, Abortive ova resulting from division of first polar 

 body. 4, Second polar body, abortive ovum. 5, Mature egg. 



with its discus proligerus. Like the spermatogenic cell, the ovarian 

 ovum also undergoes the karyokinetic division, but with somewhat 

 different result. We find two cells formed, one of which is very large 

 and contains the chromatin substance and the cytoplasm in the same 

 proportion as the egg cell, and another, which is very small and con- 

 tains only chromatin, and little cytoplasm. A second division of 

 the larger cell takes place, with the same result, forming again one 

 large cell and one very small one. The first small cell, in the mean- 

 time, frequently also divides in two, and, because the three small 

 cells are found grouped together on one of the poles of the large 

 cell, they received the name polar bodies. They take no part in the 

 processes following, and gradually disappear. The large remaining 

 cell is the mature ovum, the one which is qualified for fertilization, 

 and the series of changes through which the ovarian ovum has to 

 pass to become so qualified is called maturation. The parallelism in 

 the changes which take place during formation of the two sexual 



