i6 INTERNAL SECRETIONS OF THE OVARY 



actual cell destruction is involved, it seems probable that the 

 secretion is the manifestation of a katabolic phase resulting 

 from withdrawal of a growth stimulus. 



The number of mammae and their distribution varies 

 widely in different species. The smallest normal number 

 appears to be one pair, while in the larger polytocous animals 

 (pig), as many as six to nine pairs may be found. The rat, 

 rabbit and mouse have five to six pairs. Where there are only 



a. 





•>!•. ^ 



■-^'Vi 



'^-i ' 



vrti »»•►"» -•> ' 



T> 



^«.-:~^ 



.•»!- .,^ 







■ a.i. 



c.t. 





Fig. 9. — Lobule of Mammary Gland of Cow. 

 a. alveolus; a.i. adipose tissue; c.t. connective tissue. 



one or two pairs they may be either thoracic (Primates, elephant) 

 or abdominal (guinea-pig, cow, etc.). The presence of a large 

 number of mammae involves their distribution over both thorax 

 and abdomen. In certain animals the mammae have milk 

 reservoirs, which involve alterations in the shape of the gland, 

 resulting in the udder typical of ruminants. The rat, mouse, 

 rabbit, and ferret, on the other hand, have no receptacles for 

 the milk beyond the ducts, which may become greatly 

 distended; the glands in these animals are flat strips of tissue 

 beneath the skin. In the rabbit the gland can readily be 

 stripped off from both skin and body wall and can be prepared 



