320 



VERTEBRATE ANIMALS. 



one of the muscles of the abdomen. There ai'e no external ears. 

 The mammary glands have no nipples, but open either on a flat sur- 

 face {Ornithorlii/iichus), or into a small " mammary pouch " (jEc'/ii'dwa). 

 It has recently been shown by Mr Caldwell that the jNfonotremes are 

 not viviparous, as all other Mammals are, but that they resemble 

 the Reptiles and Birds in being oviparous. The Duck-mole lays two 

 eggs — about three-quarters of an inch in length — which it deposits 

 in the buri-ow in which it lives ; ami the Echidna lays one such egg, 

 which it is stated to place in the small pouch of skin surrounding the 

 openings of the mammary glands. Recent observations also show 

 that the Monotremes further resemble the Reptiles in the fact that 



Fig. 226.— A, Skull of Echiihui Jiysirix. B, Bide view of the skull of Ornithwhyndnts 

 paradoxus, and C, lower jaw of the saiue, viL'Avcd from above, showing the horny 

 dental plates (?u). 



the temperature of the body is much below that of the remaining 

 types of the Manmials. 



Of the two living genera of Monotremes, the Duck-mole {Ornitho- 

 rliy iii-Inis) is found exclusively in Australia inhabiting streams and 

 ponds, in the banks of which it constructs burrows forty or fifty feet 

 in length. The body is like that of a small Otter, covered with a 

 short brown fur, and having a broad flattened tail (fig. %Ti). The 

 jaws have no teeth, but cany horny jilates, which officiate as teeth 

 (fig. 226, B and C). The margins of the jaw are also sheathed in 

 horn, forming a kind of flattened beak, very like that of a Duck 

 (fig. 227). Hence the name of " Duck-billed Animal " .sometimes 

 given to the Ornkhorliynrhns. The feet are webbed, and the males 



