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 
Fic. 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. 
