INSECT-EATERS, RODENTS, AND BATS. 293 



The Rodent type is likewise found perfected at the 

 beginning of the Tertiary period. It may be said 

 that it was then less specialised, that most of the 

 Rodents of those days were more carnivorous than 

 the majority of our day, or, at least, more omni- 

 vorous ; however, little is to be gained from this for 

 our present enquiry. 



The dentition of the Rodents appears to be 

 prepared, and almost perfectly attained, by the 

 Marsupials ; l and thus in following their tracks 

 we are again referred to the Jura period, and even 

 further back, where the separation of an already 

 developed mammalian fauna had taken place : into 

 Marsupials (as the main group), Rodents, and 

 Insect-eaters. 



The latter order, no doubt, gave rise to the Bats, 

 which have fluttered about in their present shape 

 since the Eocene period. Two of our most common 



1 A comparison of the very different shapes of the molars in 

 the Rodents among one another, and the approximation of many 

 of the genera not as yet decided Rodents to the Rodent type 

 (for instance, the wombat, the fingered-animal, and rock coney) 

 renders it extremely probable that even our present Rodents are 

 not of one and the same origin. ' The fact remains, animals of 

 different derivation have attained a similar exterior, succeed 

 extremely well in the struggle for existence, or even better in 

 their endeavour to obtain food. Unlike as they may be, in one 

 point they are incontestably alike, i.e. in the development of 

 continuously growing incisors.' BAUME. 



