THE MIGRATIONS OF MAMMALS. 235 



mammals for various reasons. Males, particularly old males, are 

 more inclined to roam about than the females and the young of 

 their species, and forsake one district for another without apparent 

 reason; the younger males among gregarious species are often driven 

 out and forced to wander by the old leaders of the herd; mothers 

 with their young are fond of rambling about the neighbourhood 

 where the latter were born; and the two sexes wander about in 

 search of one another. During such expeditions the animal chances 

 to light on what seems to him a promising dwelling-place, a district 

 rich in food, a sheltering thicket, or a safe hiding-hole. He stays 

 there for some time, and, finally, it may be, settles down in this new 

 Canaan. Experienced sportsmen know that a preserve in which all 

 the game has been shot will sooner or later receive reinforcements 

 from without, and, under favourable circumstances, will be peopled 

 anew ; and all must have noticed that a fox or badger burrow is not 

 easily destroyed, for it finds new occupants again and again, how- 

 ever ruthless the persecution to which they may be subjected. As 

 it is with game, whose coming and going, appearing and disappear- 

 ing are noted by thousands, so is it with other mammals which are 

 less eagerly watched. A constant emigration and immigration can- 

 not be denied. In consequence of this, the range of distribution of 

 any species is constantly being extended, unless hindered by physical 

 conditions, or by human and other enemies. 



Till the end of the first half of last century our forefathers 

 shared their dwellings with the black rat, and knew the brown rat 

 only by hearsay, if at all. The first was a rat with many, but not 

 all the vices of its race. It lived in our houses, ate grain, fat, and 

 all kinds of provisions, gnawed doors, boards, and furniture, racketed 

 at night like a noisy ghost through old castles and other spook- 

 favouring buildings, caused much annoyance, many a fright, 

 strengthened superstition and the fear of ghosts in many a mind ; but 

 it was possible to live with it, one could manage to get along. A 

 capable cat held it in check; a skilful rat-catcher was more than a 

 match for it. Then its most terrible enemy appeared, and its star 

 began to wane. In 1727, swarms of brown rats, which seem to have 

 come from India, either directly or by way of Persia, were seen to 



