242 



REDUCTION OF THE CHROMOSOMES 



division from the egg-mother-cell (oocyte) in the same manner as the 

 spermatozoa are formed from the sperm-mother-cell (spermatocyte). 

 But while in the latter case the products of the division are all used 

 as functional spermatozoa, in the former case one of the products 



Fig. 119.— Diagrams showing the essential facts of reduction in the male. The somatic num- 

 ber of chromosomes is supposed to be four. 



A. B. Division of one of the spermatogonia, showing the full number (four) of chromosomes. 

 C. Primary spermatocyte preparing for division ; the chromatin forms two tetrads. D. E. F. First 

 division to form two secondary spermatocytes each of which receives two dyads. G. H. Division 

 of the two secondary spermatocytes to form four spermatids. Each of the latter receives two 

 single chromosomes and a centrosome which passes into the middle-piece of the spermatozoon. 



of the egg-mother-cell becomes the Q,gg, appropriating to itself the 

 entire mass of the yolk at the cost of the others which persist in 

 rudimentary form as the polar bodies." ^ 



1 ' 



'90, I, p. 126. 



