Classification of the Mammalia. 55 



LrENCEPHALA. 



In the Lyencephalous Mammalia some have the ' optic lobe ' 

 simple, others partly subdivided, or complicated by accessory gan- 

 glions, whence they are called ' bigeminal bodies.' The Lycene 

 phala with simple optic lobes are ' edentulous' or without calcified 

 teeth, are devoid of external ears, scrotum, nipples, and marsupial 

 pouch : they are true ' testiconda;' they have a coracoid bone 

 extending from the scapula to the sternum, and also an epicora - 

 coid and episternum, as in Lizards ; tbey are unguiculate and 

 pentadactyle, with a supplementary tarsal bone supporting a per- 

 forated spur in the male. The order so characterized is called 

 ' Monotremata,' in reference to the single excretory and genera- 

 tive outlet, which, however, is by no means peculiar to them 

 among Mammalia. The Monotremes are insectivorous, and are 

 strictly limited to Australia and Tasmania. 



The Marsupialia are Mammals distinguished by a peculiar 

 pouch or duplicative of the abdominal integument, which in the 

 males is everted, forming a pendulous bag containing the testes ; 

 and 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 

 number of incisors, but usually including 4 true molars ; and never 

 more than 8 premolars : the angle of the lower jaw is more or 

 less inverted. 



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

 can, 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 mammalian 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 conti- 

 nent abound. We may associate with their low position in the 

 mammalian scale the prevalent habit amongst the Marsupialia of 

 limiting the exercise of the faculties of active life to the period 

 when they are shielded by the obscurity of night. 



