FUNCTIONAL VARIATION 107 



SECTION IV NORMAL FUNCTIONS EXERCISED 

 UNDER ABNORMAL CONDITIONS 



The mammary gland, normally confined to females, is com- 

 monly functionless until after pregnancy ; but by manipulation 

 of the udder, heifers and other females may be made to yield 

 milk without bearing young. Again, rudimentary mammae, 

 present generally in males, are occasionally accompanied by 

 considerable development of mammary tissue, nearly always 

 but not necessarily functionless. 1 



Most remarkable of all, mammary-gland tissue has been 

 known to develop in extremely unusual places upon the body. 

 Mammary tumors in the axilla (armpits) are described as of 

 " common occurrence in lying-in women." 2 These tumors have 

 no duct, but in squeezing they yield " both colostrum and 

 milk," following in the same order as from normal mammas, 

 and oozing through the skin " at the situations of the sebaceous 

 follicles." 



Besides these there is " indisputable evidence of the presence 

 of a mammary gland on the thigh . . ., on the cheek . . ., on 

 the acromion (shoulder point) . . ., and in the labium majus. 

 ... In the two last cases the mammary nature of the gland 

 was proved by microscopic examination." 3 



Similar conditions may be produced artificially by grafting, 

 and all sorts of abnormalities may testify to the persistence 

 with which highly specialized tissue continues to discharge its 

 functions, often under the most discouraging circumstances. 4 



For example, Hunter and Duhamel grafted the spur of a 

 young cock into his comb, " where it continued to grow to its 

 normal size." 5 " Bert transplanted the tail of a white rat to 

 the body of Mus decumanus (the common brown rat), where it 

 continued alive." 5 The same experimenter bent over the tail 



1 Dr. Hottes, a personal friend of the writer, knew a young man in Germany 

 who was suckling an infant. 



2 Bateson, Materials, etc., p. 185. 



3 Ibid. p. 187. 



4 As when a piece of mammary gland was grafted into the ear of a guinea pig ; 

 when the pig became pregnant the gland commenced to secrete. 



5 Morgan, Regeneration, pp. 178-179. 



