200 Proceedings of the Royal Physical Society. 



the easy swimming habits of the reindeer by the hypothesis 

 of gradual growth throughout long generations, it was asked, 

 how has the grey squirrel not become in the same way an 

 adept ? It has not profited by circumstances, but still con- 

 tinues a bad swimmer. The third head — Partial Migrations, 

 Periodic and Seasonal — was taken up. The movements in this 

 case are from one locality to another, within a comparatively 

 limited area, yet they shed light on general migration. The 

 habits of the varying hare {Lepus variabilis) show that breed- 

 ing instincts are seasonally influential in its change of place. 

 But the periodic wandering of the roe-deer {Cervus capreolus) 

 cannot be accounted for either by the theory of breeding or 

 food. An instance was given, and it was argued that, again, 

 nothing affords a better explanation than the theory of an in- 

 herited drawing towards localities of ancestral distribution. 

 Facts connected with the periodic visits of the raven (Corvus 

 corax) were appealed to as illustrations. It was shown that this 

 theory sheds light on far wandering, and may have important 

 bearings on the presence of remote species in the quaternary 

 deposits of Britain, and also on the relations of present forms 

 to the great extinct mammals. The discovery of the tiger 

 by Von Schrenck, as an ordinary resident in Amoorland, and 

 as occurring in latitude 52° N., was mentioned in this con- 

 nection as opposed to the temperature theory of migration. 

 This view was illustrated by reference to the nesting of the 

 eider duck {Somateria mollisima) in the Forth, and in the 

 Outer Hebrides. The whole question of the influence of 

 climate, as well as of the physical features of the surface, in 

 determining the area both of the migration and of the geo- 

 graphical distribution of mammals, demands far more attention 

 than has yet been given to it. The sharp lines which enclose 

 the areas in which some of the bats live are suggestive on 

 this point. Those animals possess all the advantages which 

 the bird does, as regards power of flight. Yet many species 

 do not avail themselves of this even for purposes of 

 food. The mouse-coloured bat {Vespertilio murinus), which 

 is one of the commonest bats of France, and lives, as it were, 

 in the very sight of Britain, is rare in this country. If it be 

 said this is the result of the water boundary, we have only to 



