84 THE DETERMINATION OF SEX 



between wide limits. We have also discovered that the num- 

 ber of chromosomes in the sexual elements in every species 

 which has been adequately investigated is about half the num- 

 ber of chromosomes occurring in the somatic cells. When 

 sexual products arise from the sexual cells, each cell divides 

 twice in rapid sequence, so that four sexual elements arise. 

 When male elements arise all four cells normally develop. 

 An interesting and instructive exception will be considered 

 presently. In the case of four female elements, on the con- 

 trary, only one cell enlarges and becomes an ovum. The 

 three other cells, which have long been known by the name of 

 polar globules, break down.^ If we count the chromosomes 

 which appear during this double division, we find in typical 

 cases that their number is reduced one half, so that at the 

 close of the process we have cells, the so-caUed sexual elements, 

 which contain only half as many chromosomes as the cells 

 of the body, and the original sex cells. More careful in- 

 vestigations have taught us further that the reduction in 

 the number of chromosomes is not always exactly to one- 

 half. We find in certain cases one or several extra chromo- 

 somes. The origin and significance of these extra, or ac- 

 cessory, chromosomes has been studied especially in America. 

 American investigations have yielded the very important 

 result that the accessory chromosomes stand in immediate 

 relation to the determination of sex. To collect the facts 

 has cost many years of difl&cult labor. These facts have 

 made it clear that in all higher plants and animals we 

 encounter two fundamentally different species of cells; first, 

 ordinary cells with the full number of chromosomes; second, 

 special cells which we know as sexual elements, or sexual 



the number of chromosomes is subject to minor variations. Compare H. L. Wieman's 

 article in the number for May, 1913, of the American Journal of Anatomy. 



