II. 



Its Relations to Geology. 



As stated in my last lecture, to arrive at anything like 

 a fair comprehension of the relations of biology to geol- 

 ogy, we must first gain some general understanding of 

 the question of the geographical distribution of existing 

 forms of life. It was also pointed out that in order to 

 be enabled to enter upon this important subject with any 

 degree of thoroughness at all, it would become necessary 

 to limit ourselves to some one of the great branches of 

 the animal kingdom, and through it seek to illustrate the 

 main facts, as they are now known to biologists, which 

 pertain to the matter of the distribution of animals and 

 plants over the face of the globe. For this purpose the 

 vertebrata offer us as useful a group as any one thai 

 could be selected. The vertebrata, as you know, is that 

 most important branch of the animal kingdom which 

 includes all the back-boned animals, or the mammals, 

 birds, reptiles, batrachians, fishes and the like; and from 

 all these the distinguished British zoogeographer, Mr. A. 

 R. Wallace, chose the first class or the mammalia from 

 which to deduce the principles of the science of zoogeo- 

 graphy. Upon applying these principles to other great 

 groups of animals and to plants it has been found that in 

 the main they are in ha-mony with them, and where 

 decided exceptions exist they serve to explain questions 

 that would otherwise be in doubt. 



Now zoogeography is a scheme by means of which we 

 can classify our knowledge of animal distribution and in 

 an orderly manner present it to the mind so that it can be 

 easily appreciated. Many scientists have devoted years 

 of study to this subject alone, and among them we must 

 not neglect to mention, in addition to Mr. Wal- 

 lace, already referred to, the names of Buffon, the 

 eminent French biologist, Agassiz, Allen, Gill, of this 

 country, Sclater of London, and Alexander Yon 

 Humboldt. In the present connection, however, it 



