568 MAMMALS. 



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. They are 

 obviously well-protected by their spines, and are very hardy. 



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. 



Sub-class Metatheria or Didelphia, — Order Marsupialia. 



With the exception of the N. American opossums, 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 

 indigenous to Australasia, it seems as if the insulation of 

 that region had occurred after the Marsupials had gained 

 possession of the region, but before any mammalian com- 

 petitors had appeared on the scene. Thus saved and insu- 

 lated, the Marsupials have developed in many different 

 directions, the families included in this order being very 

 diverse. 



General Characters of Marsupials. — The brain is less 

 evolved than in higher mammals, for the convolutions are 

 simple or absent, the anterior commissure is large, the 

 corpus callosum is still small. In the skeleton there are 

 several peculiarities ; thus the angle of the lower jaw is more 

 or less inflected, except in the genus Tarsipes; there are 

 generally two epipubic or " marsupial " bones in front of the 

 pubic symphysis ; there are more incisors above than below 

 (except in the wombat), and the number of incisors some- 

 times exceeds three on each side. A common sphincter 

 muscle surrounds the anus and the urinogenital aperture, 

 and in the females (except kangaroos) the anus lies so much 

 within the urinogenital sinus that the arrangement may be 

 described as cloacal. The scrotal sac containing the testes 

 lies in front of the penis. The genital ducts of the females 

 are often separate throughout, so that there are two uteri and 

 two vaginae. But the bent proximal parts of the vaginae 



