130 



BIOLOGIC BASIS OF SEX 



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Fig. 2.34. The normal development of the mammary rudiments in embryos of the field 

 mouse, and the effects of sex hormones (for a summary see Raynaud, 1950). A. Early appear- 

 ance of the mammary thickenings in the female (left) and the male (right). B. Later stage, 

 showing growth of the mammary primordia and penetration into the mesenchymal layer. C. 

 Stage of sexual differentiation: in females the mammary rudiment remains attached to the 

 epidermis and the nipple later develops at this point; in males the rudiment becomes de- 

 tached from the epidermis and persists as a small epithelial nodule in the underlying 

 mesenchyme. For the effects of hormones and of castration on this pattern see text. D. Nip- 

 ple development in a male embryo induced by treatment of the mother with estradiol di- 

 propionate. For details see text. (After A. Ravnaud, Arch. Anat. micro.scop. et Morphol. cx- 

 per., 39, 518-569, 1950.) 



