Permanence and Evolution. 149 



Marsupials came respectively from one imme- 

 diate stock, then the characters which, e.g., 

 the thylacine has in common with Canis, 

 and so on, must have been independently de- 

 veloped. 



A similar case he gives is that of the relations 

 of the Carinate birds (all, except the ostrich 

 family) with the ancient Pterodactyle reptiles 

 on the one hand, and of the ostriches with the 

 ancient Dinosaurian reptiles on the other. Here, 

 again, there is the same alternative. Either birds 

 had two origins, so that the distinctive characters 

 of the class were independently produced, or all 

 birds originated from Pterodactyle reptiles, and 

 the characters common to ostriches and dino- 

 sauria originated independently, or all birds 

 sprang from Dinosauria, and the similarities 

 between Carinate birds and Pterodactyle reptiles 

 were separately evolved. These instances Mivart 

 considers " a dilemma, either horn of which bears 

 a threatening appearance to the exclusive sup- 



