Class 6. Mammalia. Order 2. Marsupialia. 



497 



immediately after birth ; they are each attached immovably by 

 suction to one of the mammillge for a long time. 



The dentition of the Marsupials on the whole resembles that of 

 other Mammals ; they differ, however, in some points. The molars 

 vary within the number seven in each haK of the jaw. Only a single 

 form with degenerate teeth has a larger number ; the incisors 

 may, however, be as many as five aboye, four below. Of the seven 

 molars the third alone has a predecessor, the only milk tooth met 

 with so far in this group. The form of the teeth, especially of the 

 molars, varies considerably in correlation with very diverse habits. 



In most points of sti-uoture the Marsupials stand nearei- the placental 

 Mammals than do the Monotremes ; mammillae are present, the coraooid is 

 rudimentary, there is no epistemum, the cochlea is spirally coiled, the penis is 

 essentially like that of the placental Mammals, the testes move back into a scrotum , 

 the ovum is very small, and segmentation is total, etc. 



Most existing Marsupials live in the Australian region, the 

 Opossums* alone inhabit America. In earlier geological times, 

 however. Marsupials occurred also in other parts of the world. 



At least three small 

 similar incisors on each 

 side of the lower jaw. 

 The canines larger than 

 the incisors. 



Only one large incisor 

 in each ramus of the 

 lower jaw. The canine 

 small or absent. 



Op ossnms. 

 Bandicoots. 



Kangaroos. 



r 



None of the toes of 



I the hind leg united. 



Toes 2 and 3 thinner 

 } than 4 and 6, and united 

 together. 



1. Opossums {Polyprotodontia). Four or five incisors in the upper, 

 three or four in the lower jaw. Well developed conical canines. Molars with 

 cusps or tubercles. The second and third digits of the hind foot are like the 

 fourth and fifth, and are not united. 



(a.) The True Opossums {Didelphyidse) have, on the hind foot, a weU- 

 developed, but clawless, hallux which can be opposed to the rest of the toes; 

 i s^, c \ m ^. Tail long and prehensile, almost naked, but scaly. The pouch 

 is weU. developed in some foi-ms, rudimentary or wanting in others. They feed 

 upon Insects, and are small animals, living exclusively in the New World, 

 chiefly in South America. 



(6) Native Cats, etc. [Basyurids). Hallux rudimentary or absent. 

 i i. Tail not developed as a prehensile organ, Carnivorous or insectivorous. 

 Among them the peculiar Native Oat [Dasyurus), and the long-legged, 

 wolf -like Tasmanian Wolf (Thylacmus), occun-ing only in Tasmania. 

 Pm-ther, the small squirrel-like Marsupial Ant-eater (Myrmecobius), 

 with f small molars, and with long, smooth protmsible tongue. 



2. The Bandicoots (Peramelina) resemble the preceding group as 

 regards the teeth, whilst they agree with that following in the stmcture of the 

 hind feet, for the second and third toes are thin and enclosed in a common 



* The forms cited below, which are not specially commented on, live in Australia 

 (some of them also in New Gruinea, Tasmania, etc.). 



E K 



