258 MAMMALS. 



that it does not exist mucli to the north of the great lakes. He also found specimens in Florida 

 and Texas. Lichtenstein found it in Mexico, and it is in M. Salvin's Kst of species found in 

 Guatemala. Besides it three other species are found in North America. A larger species (P. 

 SABRixus) replacing it in Lower Canada. Neither it nor any other species, however, is found in 

 South America. None are found in Africa or Southern Eurojje. 



Pteromts. (Map 80.) This section is confined to India, chiefl}^ the Nejiaid, Sikkim, and other 

 Hiuunalayan districts, and to Java and the rest of the Indian ArchijDelago. It num.bers only six 

 or seven species. 



The numerical proportion of the species of Squirrels and Flying Squirrels in the different quarters 

 of the world, may perhaps furnish some data for determining the site of their original birth-place, or 

 sj)ecific centre, and the course of their subsequent dispersion. These have a more imcertaiu basis 

 than they would otherwise have had, owing to the variable character of many of the species, and our 

 consequent ignorance of their true numbers ; still we can make out something from them even here. 

 Generally speaking, I do not attach great weight to numerical statistics of this nature : in the first 

 place, because I know that they must be wrong ; the estimate of what a species is being constantly 

 inconstant, and invariably varying according to the bias of the author who describes it. In 

 this instance. North America, on the one hand, has had her lists purged of half her species by 

 Baird, and India on the other has had hers doubled by Hodgson and Blyth. Had both been dealt 

 with by the same men the proportion would have been preserved, but here the balance is quite 

 upset. In the next place I regard them less, because we can never tell to what cause the pre- 

 ponderance of species is due. The presence of species is something ; it is a positive fact ; their 

 absence is nothing, or at best onlj^ half something. The species may have been present, where it is 

 now absent, and in greater numbers than any others elsewhere ; but a flood, or a sinking of the land 

 for four-and-twenty hours, or a famine, or a pestilence, — a rinderpest, may have swept them all 

 away. It is therefore only when they are very marked that numerical statistics can be at all 

 trusted to, and even then they must be used with great caution. Notwithstanding what I have 

 above said they are stUl well marked in the Squirrels, and the following facts stand out suffi- 

 ciently clear and positive to allow us to reason from them. We have the positive fact that they 

 are found in every region of the world, except Australia and Madagascar. It may be assumed 

 as proved, too, that a greater number of species is fovmd in India and the Malayan Archipelago 

 than anywhere else ; and the reader will remember that that is the region nearest to the laud of 

 their equivalents the Marsupial Petauri. Probably the half of them are foimd there ; a third 

 may inhabit North America ; Africa and South America may each have about a ninth or a tenth ; 

 and Europe and Northern Asia are limited to the single species found in Britain. 



The Indian Archipelago seems, therefore, to have most right to be considered the starting- 

 point, or specific centre of the family ; and if so, it is plain that a swarm must have been thrown 

 ofi" from thence, which, somehow or other, has reached North America. How can they have got 

 there ? Can the transition have been made bj^ Sciuropterus volans, the European and Asiatic 

 species, di-awing its origin from India, extending to America, by the Bhering Straits route, 

 or some neighbouring jDassage, and tlien becoming changed into So. volucella? It is against 

 this idea that So. volans is not found east of the Lena nor west of the Gulf of Finland. 

 It rather looks as if it were an ofishoot from some of the Himmalayan species going north- 

 wards, and spreading a little to the right hand and to the left. In speculating on this we ' 



