WHEN DEVELOPMENT GOES WRONG 



139 



Milk secretion is the function of glands that are normally 

 confined to special parts of the body. It is not unknown, how- 

 ever, that the tissues of various parts of the body, especially in 



Fig. 24. Abnormal horny growth on the head of a deer. Specimen in 

 State Museum, Augusta, Maine. Courtesy of the superintendent 



the region of the lymphatics, may alter their function and 

 secrete real milk. 



This development of a part out of place is not common, but 

 it occurs frequently enough to show the fact that each part of 

 the body is a kind of definite unit quite independent of other 

 parts, all of which casts important light upon the semi-independ- 

 ent nature of unit characters. 



