METATHERIA, DTDELPHIA, OR MARSUPTAUA. 685 



The duckmole, or duck-billed platypus, lives beside lakes and rivers. 

 It swims by means of its fore-limbs, which are webbed as well 

 as clawed ; it grubs for aquatic insects, crustaceans, and worms, in 

 the mud at the bottom of the water. It collects small animals in its 

 cheek pouches, and chews them at leisure with its eight horny jaw- 

 plates. It makes long burrows in the banks, often with two openings, 

 one above, one under the water. The animal is shy, and dives swiftly 

 when alarmed. When about to sleep, it rolls itself into a ball. In the 

 recesses of the burrows the eggs are laid, two at a time. The egg 

 measures about three-quarters of an inch in length, and is enclosed in a 

 "strong, flexible, white shell," through which the young animal has to 

 break its way. 



The full-grown duckmole measures from 18 to 20 in. in length ; 

 the male slightly exceeds his mate. The fur is short and soft, 

 dark-brown above, lighter beneath. The jaws are flattened like the 

 bill of a duck, and covered with naked skin, which forms a soft, 

 sensitive collar around the region where the bill joins the skull. The 

 eyes are very small ; there is no external ear-flap or pinna ; the nostrils 

 lie near the end of the upper part of the bill. The tail is short and flat. 



True teeth, three on each jaw above and below, are calcified, last for 

 about a year, and are then lost, being replaced by horny plates, two on 

 each jaw, above and below. The spur borne on the heel seems to be 

 sometimes used as a weapon, and as it persists only in the males, is 

 perhaps useful in contests between rivals. 



Echidna and Proechidna live in rocky regions, are mainly nocturnal 

 in habit, and burrow rapidly, legs foremost. They feed on ants, which 

 are caught on the rapidly mobile, slender, viscid tongue. No traces 

 of teeth have as yet been seen. 



Strong spines occur thickly in Echidna, more sparsely in Proechidna 

 among the hairs. The snout is prolonged into a slender tube. The 

 limbs bear five toes, two of which in Proechidna are often without 

 claws and somewhat rudimentary. In Echidna the eggs seem to be 

 hatched in a temporarily developed pouch. 



The Allotheria or Multituberculata include small extinct Mammals 

 (from Triassic to Eocene) with multituberculate molars, e.g. Plagiaulax, 

 Microlestes, Tritylodon. 



Sub-class Metatheria, Didelphia, or Marsupialia. 



With the exception ot the American opossums, and 

 a little-known mouse-like animal (Canolestes) from S. 

 America, all the Marsupials now alive are natives of 

 Australasia. But fossil remains found in Europe and 

 America show that they once had a wide range. As 

 there are no higher Mammals indisputably indigenous to 

 Australasia, it seems as if the insulation of that region had 

 occurred after the Marsupials had gained possession, but 

 before higher mammalian competitors had arrived. Thus 



