98 MAMMARY APPARATUS OF THE MAMMALIA 



potaraus the nipples occupy a similar dorso- 

 lateral position, and it is asserted that the 

 young, sitting on the back of the swimming 

 mothers, can in this way get their food in 

 comfort. 



Further, it has long been remarked that 

 there is not always a constant number of 



Fig. 36. — Dorso-Lateral Arrangement of Nipples 

 AS IN Myopotamus Sp. (Embryo). 



nipples in individuals of the same species. 

 In many species the number of nipples has 

 a wide range of variation — for example, in 

 the pig, where they vary between eight and 

 eighteen, 30-40 per cent, possessing twelve. 

 This phenomenon, which is also observable in 

 some of the lower Didelphyidae, I have termed 



