524 



MAMMALIA. 



all make s])e('ial nests for their brood, which they often line with 

 soft materials ; some even construct true nests, like those of 

 birds, of grass and stalks. Many of those which inhabit sub- 

 terranean holes and passages store up winter provisions, 

 which they consume in the sterile season, or in autumn 

 and spring (winter-sleepers). 



Geographical distribution.* Some orders, as tlie rodents and 

 bats, are represented in all parts of the world. Of the Cetacea 

 and Pinnipedia most species belong to the polar regions. In 

 general, the Old and New Worlds have each their own fauna. 

 The mammalian fauna of Australia consists almost exclusively 

 of marsupials. The oldest fossil remains (lower jaw) of mam- 

 mals are found in the Trias (Keuper Sandstone and Oolite, 

 Stonesfield slate) and are supposed to belong to the Marsupialia 

 (p. 539). But it is not until the Tertiary period that the mam- 

 malian fauna presents a rich development. 



The classification of Mammalia adopted in this work is as 

 follows : — 



* Wallace, Sclater, Lydekker, op. cit. f Extinct. 



