THE GERM-CELLS 



^9 



o 



difference is this : that each of the two daughter-cells does 

 not receive, as happens in the regular Karyokinesis, the 

 same number of chromosomes as the mother-cell. Indeed, 

 no splitting up of the chromosomes lengthwise takes place 

 for that purpose, but each daughter-cell receives only half 

 the original number of chromosomes — i.e., in our case, as 

 the ripe ovum had eight chromosomes, the ovum, as well 

 as the first polar body, have after the first division four 



ME12 Eiz 



Fig. 28. — Maturation of Parthenogenetic Ovum. 



{From Weismann, " The Evolution Theory.") 



Uei, primitive ovum with four chromosomes ; MEiz, mother egg- 

 cell with eight chromosomes ; Eiz, formation of one polar 

 body (Rk^). 



chromosomes each. But now a second division is neces- 

 sary, in order to reduce the number of chromosomes still 

 further to half the original number of the primitive ovum, 

 which had four chromosomes. This takes place in the 

 same manner as just described for the formation of the first 

 polar body. The remaining chromosomes of the ovum 

 divide again, two now remaining finally in the ovum, and 

 two forming a new polar body. As the first polar body 

 also has meanwhile divided into two, each with two 

 chromosomes, we have as the final product of maturation 

 the ovum with two chromosomes (being half of the original 



