THE FIRST MAMMARY ORGANS 39 



thereto. Simultaneously the hrooding period 

 grew continuall)' shorter, and the original 

 purpose of the brooding organs — namely, the 

 production of warmth for the young — was lost. 

 And so the rich supply of bloodvessels to these 

 organs favoured the development of the tubular 

 glands in these regions, so that from the very 

 commencement they were able to produce a 

 stronger secretion than the rest of the skin 

 glands. Accordingly, when the primitive 

 mammals attained to that evolutionary phase 

 in which the young, hatching out from the 

 egg in a quite immature condition, required 

 to be fed by the mother, that need could at 

 once be supplied by the gland complexes of 

 the areas of the original brooding organs. 

 Thus, too, in the case of the Prototheria, the 

 first mammary organs sprang from the former 

 brooding organs as circumscribed parts of the 

 abdominal skin, characterized by the possession 

 of strong hairs, the mammary hairs, and by 

 glands opening out of these, strongly de- 

 veloped, and hence well fitted for quicker 

 secretion. 



In this form arose the mammary apparatus 

 uniformly in the case of all Prototheria. But 



