MAMMALS 



477 



been derived from the former (sweat-glands), those of other 

 Mammals from the latter (sebaceous glands). 



During the egg-laying season a sort of pouch develops on 

 the under side of the Spiny Ant-eater, into which the milk- 

 glands open (fig. 995). To this the single egg (about f inch 

 long) is transferred by the mother, by means of her snout. 

 After a short incubation the young animal breaks through the 

 egg shell with the aid of a little knob on its nose, something 

 like that present in a young bird, and the mother is also said 

 to give assistance. The little creature is entirely devoid of 

 hair and not much like the adult (fig. 996). It is sheltered 

 in the pouch till about 

 three inches long, and 

 feeds by licking up the 

 milk which is secreted. 

 The preceding facts are 

 chiefly due to the inves- 

 tigations of Semon, who 

 gives the following ac- 

 count of subsequent 

 events (in In the Aus- 

 iralian Biish): — "From 

 the middle of October 

 my blacks found several such older specimens outside the maternal 

 pouch in little hollows of the ground. . . . The blacks all told 

 me that the ' old woman ' (as the natives call the mother animal) 

 during the first weeks often returns to the young one to take it 

 into her pouch and suckle it. On entering upon her nightly 

 rambles, however, she deposits her weighty and inconvenient 

 youngster, digging a little burrow for it, where she stows it away 

 until her return from her roamings. I was able to substantiate 

 this account. ..." The very intimate relation between mother 

 and offspring which suckling entails has probably played an im- 

 portant part in the evolution of the pronounced maternal affection 

 for which Mammals are remarkable. 



The aquatic Duck- Bill (Ornithorhynchus) digs out a burrow 

 of from 20 to 50 feet in length, the inner end of which is 

 enlarged, much as in the dwelling of a Kingfisher or Sand- 

 Martin. The main opening is under water, but there is a 

 second one above the surface, which appears to promote venti- 



Fig. 996. — Pouch (c, in section), bunch of milk-glands [a], and 

 Pouch-Embryo [e] of Spiny Ant-Eater {Echidna). The openings 

 of the glands into the pouch are shown. 



