126 



BIOLOGIC BASIS OF SEX 



Fig. 2.32. The effects of sex hormones on the sex type of tlic copulalory stniciur(-s in 

 young opossums. A. The appearance of the phallus, or genital luljerclc, ui ;i normal male 

 (left) and female opossum aged 20 days. Sex is difficult to distinguish by form alone but the 

 phallus is somewhat larger in the male. Sex is readily distinguished at this age, however, by 



