MAMMALS. 



379 



prolongation of the larynx into the choana, much as in the whales. 

 In development the ova pass into the uterus, from which they 

 absorb nourishment without the intervention of a 

 placenta (except in Perameles), no villi A,A 



being developed on the serosa, and ■'•■'-^ 



the allantois failing to reach this 

 envelope. An osteological pe- 

 culiarity, present in all except 

 in Tarsipes, is the inflection 

 of the posterior angle of the 

 jaw. 



In size the marsupials 

 vary from animals the size 

 of a rat, up to the giant 

 kangaroo ; while in the past 

 Diprotodoii was as large as 



Fig. 357. Skeleton of kangaroo, from Macallister. 



a rhinoceros. In form and habits they show many modifica- 

 tions, usually attributed to the fact that in Australia they 

 have been removed from competition with other mammals, and! 

 have developed in every direction, — terrestrial, crawling, leap- 

 ing, climbing, and soaring forms. The majority are nocturnal. 



Sub-Order i. Polyprotodontia. 



Incisors 1, small, subequal ; canines larger: molars acutely tuber- 



4 or 3 



culate. 



The DidelphiDjE, opossums, American ; teeth i \,c\,p\,m\\ feet all 



five-toed ; tail partially naked and usually prehensile. Didelpkys virginiana, 



north to New England ; other species in the tropics. Chironectes has webbed 



feet. Didelphys occurs in the eocene of France and America. DasyuriDjE 



/ 4 c-,i)^-^—^,w^^\ hind feet four-toed. Thylacinus is dog-like, 

 3' I '^ 2 or 3 4-6 



carnivorous, and occurs in Tasmania. Myrmecobius with m f , feeds on 



ants. Dasyiirus, Phascogale. Allied forms fossil in lower tertiary of South 



America and later tertiary of Australia. The PerameliD/E, i \, c \, p f , 



