EGG-LAYING MAMMALS, OR MONOTREMES. 165 



abundance of spines in the fur. The New Guinea, or 

 Three- toed Echidna, is larger than many specimens of 

 the common species, and usually has but three claws 

 to each foot. 



Echidnas are usually found in rocky and mountain- 

 ous districts, and are of nocturnal and burrowing 

 habits ; their powerful claws enabling them to bury 

 themselves in the ground with extraordinary rapidity. 

 If dug out from their burrows during the day, they 

 appear sluggish and stupid, crouching to the ground 

 with the head between the legs, and thus presenting a 

 mass of spines to an enemy. The eggs of the Echidna 

 have, indeed, been found and described ; but it appears 

 that the development of the young is less well known 

 than in the case of the Duck-bill. 



Having now introduced our readers to the personal 

 appearance and habits of the Duck-bill and the Echidna, 

 we are in a position to enter into the consideration of 

 some of the more striking features of their structure, 

 and of their relationship to other groups of animals. 



We have already stated that these creatures agree 

 with other mammals in suckling their young from 

 milk-glands on the body of the female parent, and are 

 therefore rightly included in the great class of Mammals. 

 They also agree with other mammals in that the skull 

 articulates with the first joint of the back-bone, or 

 first vertebra, by means of two knob-like prominences 

 known as condyles. In this respect they differ from 

 Birds and Eeptiles, in which this articulation takes 

 place only by a single condyle; but it is very note- 



