122 PRIMITIVE ANIMALS 



milk ; the skeleton is essentially Mammalian, though 

 with certain Reptilian reminiscences, especially in 

 the limb girdles, and a Reptilian condition is still 

 preserved in the fact that the apertures of the 

 rectum and of the urino-genital system open into 

 a common cloaca, whereas in the higher Mammals 

 these apertures are always separate. It is, however, 

 in the mode of reproduction that the Monotremes 

 have retained the most undoubted traces of their 

 Reptilian ancestry, since, instead of nourishing the 

 foetus in the uterus by means of a placenta, they lay 

 eggs which they hatch out in a nest. 



The Echidna, known to the Australian settlers as 

 the Native Porcupine, is a small animal, sometimes 

 attaining two feet in length ; it is covered with sharp 

 quills and has the power of rolling itself up into a 

 prickly ball when it is in fear of an attack. The jaws 

 are prolonged into a very long snout, and the tongue is 

 long and extensile, these characters being adapted to 

 secure the ants on which the creature subsists. The 

 limbs are very stoutly built and fashioned for digging, 

 since the animal not only must burrow for its prey, 

 but it also excavates a hole in the ground, usually 

 under a rock or tree-stump, where it makes its nest. 

 The female Echidna deposits a small egg with a 

 leather} 7 shell, resembling that of a Reptile ; it is 

 transferred, after being laid, to a small pouch on the 

 under surface of the female which develops only at 



