214 THE MEANING OF EVOLUTION 



dient in the milk produced by the transformed gland. 

 But there is another important constituent. When 

 one does unaccustomed manual work the ordinary re- 

 sult is the formation of a blister. The epidermis, or 

 scarfskin, becomes detached from the dermis, or true 

 skin, and the space between the two rapidly fills with 

 the fluid portion of the blood, known as lymph. The 

 fact that no blood vessels have been broken in this 

 detachment results in there being no red corpuscles in 

 this fluid. Wherever a cavity forms in the body 

 lymph is liable to enter it. 



The milk glands of the mammals are modified oil 

 glands. The fluid which they now pour out is no 

 longer exactly the old oil with the addition of the 

 lymph. Undoubtedly in the past the first milk was 

 more like this simple mixture. There seems no doubt 

 that the breasts of to-day are the enlarged and modi- 

 fied oil glands of earlier mammals. In one of the 

 most primitive of our mammals the young simply 

 lick certain bare spots on the surface of the mother's 

 abdomen. As higher forms arise there develops a 

 smaller or larger mound with a distinct projection, 

 about which the lips of the offspring can easily fasten. 

 Lamarck would have said that the suction of the 

 infant had produced such a mound, and that this had 

 been transmitted to later offspring until it had grown 

 to be the highly developed organ we now find, for in- 



