172 GEOGRAPHY OF ANIMALS. 



the Indian Ocean ; to the beaver, an inhabitant of 

 Lapland, and found reaching as far south as the 

 Danube. Unhke the fixed and determinable position 

 of vegetables a great proportion of animated beings 

 exercise their locomotive powers at a certain season 

 of the year, and thereby enjoy an equal advantage 

 in respect of food and temperature at all times ; and 

 thus, in the removal of some, we witness the acces- 

 sion of others to the same spot : the alternate ap- 

 pearance of the summer and winter birds of passage 

 in this country serves to support this statement ; on 

 the one hand the swallow and nightingale, and on 

 the other the snipe and imber diver are familiar ex- 

 amples. Moreover there are migrations, of a limited 

 extent, occurring among animals, which however 

 are never found beyond the limits of a country : thus 

 Vaillant, in his " Travels in the interior of Africa, " 

 mentions the incredible numbers of springbocks mi- 

 grating southwards, on account of the deficiency of 

 food at that season. The locusts of Africa perform 

 also, I believe, a similar internal migration. In En- 

 gland, likewise we witness the same phenomena ; par- 

 ties of ring-ouzels, flocks of chaffinches, &c., are 

 familiar instances to the naturalist, and illustrate this 

 subject. But whilst we thus contemplate the accu- 

 racy with which the departure of animals from, and the 

 return to their fonner haunts is adjusted, we find that 

 there are some also which, uninfluenced either by the 

 love of constancy or of migration, lead an uncertain 

 kind of life : and hence unusual appearances of troops 

 of birds, strao^glers, partial migration, reinforcement 

 of numbers, and so forth. 



It will be obvious, from the dependence of whole 

 tribes of birds and quadrupeds on the vegetable pro- 

 ductions of the earth ; of many kinds on the insects 

 which live on trees and plants generally ; and from 

 the circumstance of these tribes affording sustenance 

 to the carnivorous part of the creation ; that those 

 countries best provided with vegetable growth will 

 be also most frequented by animated beings : thus it 



