SHARE OF THE PARENTS IN BUILDING UP THE OFFSPRING 39 



take place, but half the number of rods move into the right and 

 half into the left daughter-nucleus without previous division, so 

 that in each daughter-nucleus the number of rods is reduced to 



half (Fig. 76). 



Although the distribution of the rods ni this manner takes 

 place twice in succession, the normal number is not, as we have 

 already seen, reduced to a quarter, because, long before the occurrence 



R^d.S 



Fig 76 Diagram of the maturation divisions of the ovum. A, primitive 

 germ-ceih B, mother-egg- cell, which has grown and has doubled the number 

 of its chromosomes. C, first maturation division. D, immediately thereafter ; 

 Bk I the first directive cell or polar body. E, the second maturation spindle 

 has been formed; the first polar body has divided into two (2 and 3).; tlie 

 four chromosomes remaining in the ovum lie in the second directive spindle. 

 F immediately after the second maturation division ; i, the mature ovum ; 

 2, 3, and 4, the three polar cells, each of these four cells containing two 

 chromosomes. 



of the first maturing division, a duplication of the rods by means 

 of longitudinal division had taken place, and thus the first division 

 difi'ers^from an ordinary division in that the splitting of the rods 

 does not take place during the process of dividing but long before- 

 hand. Only the second maturing division differs from all other 

 nuclear divisions known to us, since it is not associated with any 

 splittino- of the rods at all, but conveys half of the existnig rods 



