SQUIRRELS. 259 



must remember that oiu- date is confined to the period subsequent to the glacial epoch, for the 

 cold of that epoch cleared off almost everything both from Europe and North America, and conse- 

 quently no use can be made of any old bridge which may have subsisted between Europe and 

 America jn-ior to the glacial epoch. 



The above inference as to the course of the distribution of species extends to the true Squirrels 

 as well as to the Flying Squirrels. What has taken place in Pteromys and Sciuropterus is obviously 

 repeated in Sciurus in every point, although the contrasts are less marked, there being a much 

 larger number of species. Africa seems to have little connexion with the Indian Squirrels, from 

 which I look for the distribution of the rest. Can the communication have been by South America ? 

 No doubt there are several indications of a very ancient connexion between New Zealand and Peru, 

 especially in jjlauts and insects. It may have included the submerged continent now buoyed off 

 by the Pacific Islands, and by that route the Squirrels may have reached North America. On 

 the other hand, we have seen that there are no Flying Squirrels in South America at all. And 

 as the true Squirrels were what is called " in the same boat " as the flying ones, the specialties of 

 their distribution being merely an exaggerated repetition of the facts relating to the hitter, we can 

 hardly avail ourselves of the presence of two or three true Squirrels in South America, to explain 

 their- passage to the north. 



It must therefore have been by North America that the family established itself in the 

 New World. We may assume it as certain that there was such a connection between Asia and 

 North America by Bhering's Straits, or a little to the south of it. But the Indian Squirrel was a 

 tropical creature, and there is an absence of Squirrels in the north-east of Asia. These considera- 

 tions seem to point to another more southerly connection between Asia 'and North America, by Japan 

 and California, or stretching from China to California, in the line of the Sandwich Isles. From the 

 comparative rarity of the Squirrels in South America, and their abundance in Mexico and North 

 America, we may perhaps infer that the gap which at one time existed between North and South 

 America was present when the Squirrels established themselves in North America. That gap seems 

 to have been open and closed up more than once. 



Striped Ground-Squirrel. (Tamias.) (Map 91.) The Striped Ground-Squirrels stand between 

 the true Squirrels and the Spermophiles. Like the latter they possess internal cheek-pouches, and 

 the form of the skull is similar in a certain portion of theili. They have all a black stripe do^^^l 

 the middle of the back, and usually two others on each side ; a disposition of colouring which also 

 api^ears in some of the Mice, as Mus pumilio. Two species occur in Europe and Asia ; the 

 remainder, consisting of four or five sf)ecies, are American, one ranging from Canada to Columbia ; 

 another from the Missouri to Oregon ; one is peculiar to California, and another to New Mexico. 



For long, one species known by the name of Tamias striatus was thought to be common to 

 both Siberia and North America. More recently natirralists have come to the conclusion that 

 there are two different species, one peculiar to each continent, and Dr. Baird has named the Siberian 

 species T. Pallasii. The American animal is the larger of the two, and has the shortest tail, 

 which is more bushy and cylindrical. The coloiu- also differs somewhat, the light tints being pale 

 yellow ochre in the Siberian, and rusty brownish red, mingled with grey, in the American ; and 

 the black stripes on the back are arranged at different distances. This is Wagner's account ;* 



* Wagner, " Supp. Scbreber Saugethiere," iii. 233. 



