92 



THE DETERMINATION OF SEX 



progressive division of the cell. We notice that in each of the 

 daughter cells there is an accessory element. In ordinary 

 cell division the chromosomes form in the daughter cells a new 

 nucleus which assumes the resting form, in which we can no 

 longer distinguish the single chromosomes. In the case of the 

 developing sexual elements, however, no resting nucleus is 

 produced because the ceU at once proceeds to a second division. 



Fig. 39. — Anasa tristis. Division of the first spermatocyte, a, b, m, ordinary 

 chromosomes; x, accessory chromosomes. 



Fig. 40 shows US the successive stages of the second division. 

 During it aU the chromosomes divide with the exception of the 

 accessory, which does not divide at all, but migrates into one 

 of the cells. From the original sexual cell there have now 

 arisen four cells, two of which have an accessory chromosome. 

 The four cells change themselves into spermatozoa. In this 



