28 



duplicature of the abdominal integument, which in the males 

 is everted, forming a pendulous bag, arid in the females is 

 inverted, forming a hidden pouch containing the nipples and 

 usually sheltering the young for a certain period after their 

 birth : they have the marsupial bones in common with the 

 Monotremes ; a much varied dentition, especially as regards 

 the number of incisors, but usually including 4 true molars ; 

 and never more than 3 premolars 1 (fig. 2) : the angle of the 

 lower jaw (ib. a) is more or less inverted 2 . 



With the exception of one genus, Didelphys, which is Ame- 

 rican, and another genus Cuscus, which is Malayan, all the 

 known existing Marsupials belong to Australia, Tasmania, 

 and New Guinea. The grazing and browsing Kangaroos are 

 rarely seen abroad in full daylight, save in dark rainy weather. 

 Most of the Marsupialia are nocturnal. Zoological wanderers 

 in Australia, viewing its plains and scanning its scrubs by 

 broad daylight, are struck by the seeming absence of mam- 

 malian life ; but during the brief twilight and dawn, or by the 

 light of the moon, numerous forms are seen to emerge from 

 their hiding-places and illustrate the variety of marsupial life 

 with which many parts of the continent abound. We may 

 associate with their low position in the mammalian scale the 

 prevalent habit amongst the Marsupialia of limiting the exer- 

 cise of the faculties of active life to the period when they are 

 shielded by the obscurity of night. 



The premature birth of the offspring, and its transference 

 to the tegumentary pouch, in whicli it remains suspended to 

 the nipple for a period answering to that of uterine life in 

 higher mammals, relate to the peculiarities of the climate of 

 Australia. 



The adventurous and much-enduring explorers of that 

 continent bear uniform testimony to the want of water as the 



1 Outlines of a Classification of the Marsupialia, Trans. Zool.Soc. Vol. n. 1839. 



2 For other Osteological and Dental characteristics of the Marsupialia, see 

 the paper above cited, and that On the Osteology of the Marsupialia, Trans. 

 Zool. Soc. Vol. n. p. 379 (1838). 



