SEX 



361 



giving a female. In this case, a typical example of the XY form of sex 

 inheritance, extensive researches have shown that the y-chromosome 

 carries no factors for sex; the presence of one X-chromosome is associated 

 with maleness and that of two X-chromosomes with femaleness. Morgan 

 (1914, 19196) and Morgan and Bridges (1919) find that gynandromorph- 

 ism frequently appears in Drosophila females as the result of the 

 elimination of one sex-chromosome in abnormal mitosis. 



FIG. 140. The behavior of the sex-chromosomes in Drosophila (Stevens, Morgan, Metz), 

 Man (Wieman), Phragmatobia (Seiler), and the fowl (Guyer). 



Malone (1918) reports that there are present in the spermatocyte of 

 the dog 10 pairs of autosomes and one large unpaired X-chromosome. 

 The X passes undivided to one pole in the first mitosis and divides in the 

 second, so that half of the spermatids, and hence spermatozoa, receive 

 an X while half do not. When measurements of these spermatozoa are 

 plotted a bimodal curve results, showing that the chromosome difference 

 is correlated with a size dimorphism. The same condition, except for 

 the number of autosome pairs, is reported for the spermatozoa of horses, 

 pigs, and cattle (Wodsedalek 1913, 1914, 1920). 



In the case of man also the evidence at hand indicates a digametic 

 condition on the part of the male, but certain striking discrepancies in 

 the findings of various investigators have afforded a puzzle which up to 

 the present time has not been satisfactorily solved. Hemming (1898) 

 counted 24 chromosomes in the cells of the cornea, and Duesberg (1906) 

 found 12 in the spermatocytes. The same numbers were found by 

 Montgomery (1912). In 1910 Guyer reported that the spermatogonia 

 of the negro contain 22 chromosomes; these in the spermatocyte form 10 

 bivalents and two distinguishable accessories. At the first maturation 

 mitosis both of the latter go to one pole and at the second mitosis both 

 divide, so that half of the sperms have 10 chromosomes and half have 12; 

 the two accessories in the latter case are visible as "chromatin nucleoli" 

 in the resting stage. This difference in the gametes Guyer regarded as 

 probably associated with sex-determination. Gutherz (1912) failed to 



