2^« 









Rg. 2.12. Chromosomes from various animals. A and 5, an oogonium and a spermatogonium, 

 respectively, of the bug, Protenor, showing the two X-chromosomes of the female and the single 

 X-chromosome of the male, as well as the 6 pairs of homologous autosomes; homologous members 

 of the pairs are numbered alike: x3600. The diploid number of chromosomes in Protenor is 

 14 in the females and 13 in the males. C, two spermatids of Protenor, one of which has re- 

 ceived the X-chromosome at the disjunctional division; each spermatid has one chromosome from 

 each of the pairs of autosomes: x2900. The haploid number of chromosomes in Protenor is 

 6 in one-half of the spermatozoa, 7 in the other half of the spermatozoa and in all of the ova. 

 D and E, female and male diploid groups from Drosophila in which the chromosome number 

 is the same, 8, because the male contains a Y-chromosome : x5500. F, chromosomes of an 

 oogonium of the frog, R. pipiens, showing 26 as the diploid number: x3000. G, chromo- 

 somes of a human spermatogonium, showing 48 as the diploid number; the Y-chromosome is 

 labeled: x3480. {D and £, modified from C. B. Bridges, 1916, Genetics, vol. 1; F, from 

 C. L. Parmenter, 1925, Journal oj General Physiology, vol. 8; G, from H. M. Evans and Olive 

 Swezy, 1929, Memoirs oJ the University oJ California, vol. 9.) 



42 



