14 HEREDITY IN RELATION TO EUGENICS 



Fig. 4. — Diagrams illustrating the process of reduction of the chromosomes 

 by which half of the chromatic material is eliminated from the sex-cell. A. The 

 germ cell is beginning its penultimate division — there are four chromosomes 

 but each of them has already begun to divide to go to their respective poles, 

 as seen at B. C. The last division is taking place, but the four chromosomes 

 do not lie side by side in the equatorial plate as in ^, but they unite in two 

 pairs and, in the division, the elements of these pairs are sundered again. Thus 

 out of the original cell four ripe sperm-cells (D) each with only two chromo- 

 somes arise. FromE. B. Wilson: ''The Cell in Development and Inheritance." 



such that either the paternal or maternal component of 

 any chromosome is eliminated in the process, but not 

 both. (Fig. 5). Beyond the condition that one half of 

 each kind of chromosome must go to each daughter cell it 

 seems to be a matter of chance whether the portion that 

 goes to a particular cell be of paternal or of maternal origin. 

 It is even conceivable that one germ cell should have all 

 of its chromosomes of maternal origin while the other cell 

 has all of a paternal origin. 

 )( The important point is that the number of chromosomes 

 in the ripe germ cell has become reduced to-half and so it is 



