XIII 



PHYLUM CHORDATA 



491 



appearance of being formed by the agglutination of a number of 

 hair-like horny fibres. 



Cutaneous glands are very general in the Mammalia, the most 

 constant being the sebaceous glands (Figs. 1100, D, and 1101, HBD), 

 which open into the hair-follicles, and the sweat glands (Fig. 1100, 

 SD). In many Mammals there are, in addition, in various parts 

 of the body, aggregations of special glands secreting an odorous 

 matter. 



The mammary glands, by the secretion of which the young are 

 nourished, are specially developed cutaneous glands. In the 



g.m. 



el. 



FIG. I HI:,. Echidna hystrix. A, lower surface of brooding female; B, dissection showing 

 a dorsal view of the rnarsupium and mammary glands ; t t, the two tufts of hair projecting 

 from the mammary pouches from which the secretion flows ; bin, brood-pouch or marsupium ; 

 d. cloaca ; <j. m. groups of mammary glands. (From Wicdersheim's Comparative Anatomy, 

 after W.Haacke.) 



Prototheria they differ somewhat widely from those of the rest of 

 the Mammalia in structure, and they also differ in the absence of 

 teats. They consist of two groups of very large, tubular follicles, 

 the ducts of which open on the ventral surface. In Echidna (Fig. 

 1103) the two areas on which the ducts open become depressed 

 towards the breeding season to give rise to a pair of pouches 

 the mammary pouches. A large brood- pouch or marsupium is 

 subsequently formed, and the egg is deposited in this. When the 

 young animal is hatched it is sheltered in the posterior, deeper 



H H 2 



