SEX IN ANIMALS 



537 



swine. Wodsedalek finds that in the horse the somatic number of 

 chromosomes in the female is thirty-eight, in the male thirty-six. In 

 Fig. 211 are shown stages of the heterotypic division from which these 

 conclusions are drawn. There are apparently two accessory chromo- 

 somes, and these both go to the same pole. Consequently half the sper- 



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FIG. 211. Three figures illustrating heterotypic division in the horse. The sex-chromo- 

 somes are seen slightly separated from the autosomes in each figure. (After Wodsedalek.) 



matozoa contain nineteen and half seventeen chromosomes. No direct 

 cytological evidence of gametogenesis in the female has been obtained, 

 it is merely assumed that those gametes containing nineteen chromosomes 

 are normally female producing and that those which contain seventeen 

 are male producing. In the pig very much the same state of affairs exists. 



FIG. 212. Three figures illustrating stages in the heterotypic division in the male pig. 

 The sex chromosomes are seen passing to one pole ahead of the autosomes in the middle 

 figure. (After Wodsedalek.) 



The somatic number of chromosomes in the female is twenty, in the male 

 eighteen. In the heterotypic division in the male, stages of which are 

 shown in Fig. 212, the two accessory chromosomes pass to the same 

 pole. In consequence in the male half the gametes contain ten and half 

 eight chromosomes. From this the conclusion is drawn without further 

 evidence that the male is heterozygous and the female homozygous for 



