314 



REPRODUCTION IN ANIMALS 



conjugation of the chromosomes results in three pairs and 

 an odd or unpaired one (called a sex-chromosome) as 

 though Aa, Bb, Cc and d were the combination. Upon 

 their separation three chromosomes pass to one pole of 

 the spindle and four to the other. The two cells thus 



Fio. 77. — Diagram ilhiHtratinj? the dotx^rminntion of sox. A, 

 nucleus of Hpcrm mother cell with 7 chromosonie.s, pairing of chro- 

 moHomes with one odd (sex) chromosome. (\ division of sjwrm mother 

 cell showing 4 chromosomes passing into one cell and 3 into the 

 other. D, secpnd and last division of sperm mother cell resulting in 

 two (as yet immature) female-producing sixjrms with 4 chromosomes 

 each and two male-producing with 3 each. 



formed now divide and of the four sperm cells that are 

 produced two contain the odd number and two the even 



