THE REDUCING DIVISION 



243 



the separate members of each of the two half-tetrads 

 pass to opposite poles (Figs. 35, 36). In the nucleus 

 of each of the four cells which thus arise there is, there- 

 fore, present one quarter of each of the four chromo- 

 somes which originally appeared one member, that 

 is to say, of each tetrad (Fig. 37). Each of the cells of 

 which we have thus traced the origin develops directly 

 into a single spermatozoon. 



Fig. 38 



F.g.4-2 



The method of development, or maturation, of the 

 ova, or egg-cells, of animals is in all essential respects 

 similar to the process by which the spermatozoa arise. 

 It differs, however, in the fact that of the four cells 

 which result from the corresponding divisions, one is 

 very large and constitutes the ovum, whilst the other 

 three are very minute, and are apparently of no further 

 importance. In the accompanying diagrams (Figs. 40 

 to 42), the smaller cells, or polar bodies, have been 



16 2 



