138 TROPICAL SAVANAS 



the young. In any case the fact that, with rare excep- 

 tions, marsupials have only succeeded in surviving 

 in the Australian region, suggests that the placental 

 method, that practised by the ungulates, has been 

 justified in the struggle for existence as against the 

 marsupial method, despite the greater risk to the 

 mother before birth and at birth in the former method. 



Only one kangaroo is produced at a birth. This is 

 an interestiag point, because a reduction in the number 

 of young is frequent in animals which must escape 

 with their young by flight when threatened, and do 

 not attempt to defend themselves nor to hide. A similar 

 tendency is well marked in the higher ungulates. But 

 it must not be supposed that the kangaroo is entirely 

 helpless. In the ungulates we find that, though the 

 primary purpose of the elongation of the limb is to 

 give swiftness, yet secondarily, e.g. in the horse, the 

 powerful hind legs can be used as weapons. Similarly 

 the kangaroo can use its long hind-legs to dehver heavy 

 blows, capable of killing a dog. Like so many denizens 

 of open country, the animals are markedly gregarious. 



In regard to the other marsupials we need only note 

 that Austraha contains various forms showing special 

 adaptations to open grassy plains or desert regions, 

 these adaptations exhibiting a curious convergent 

 resemblance to those which appear among the pla- 

 centals. For example, throughout the greater part of 

 Australia the open grassy plains are inhabited by the 

 so-called pig-footed bandicoot, a small animal with 

 long hind-legs, remarkable in showing an ungulate-like 

 reduction in the number of the toes. The fore-foot has 

 two functional toes, the hind only one ; the animals 

 take both vegetable and animal food. The jerboas and 

 jumping mice of other desert regions are represented 



