306 Recent Literature. [April, 
the same direction, with the result before us, a book rather more 
popular in its treatment of the general subject, and a little narrower 
in scope in those chapters confined to a discussion of the causes 
governing the peopling of the larger oceanic and continental 
islands. The result is a most interesting work, and one which 
will serve to maintain, if not greatly advance the general interest 
felt by naturalists in the general and attractive subject of the 
philosophy or explanation of the causes of the present geographi- 
cal distribution of plants and animals. 
The author attempts to explain the present distribution of life 
by reference to a complex of causes grouped as biological and 
physical. The biological causes are (1) the constant tendency of 
organisms to. increase in numbers and to spread out, disperse and 
migrate ; and (2) “those laws of evolution and extinction, which 
determine the manner in which groups of organisms arise and 
. grow, reach their maximum, and then dwindle away, often break- 
ing up into separate portions which long survive in very remote 
regions.” The physical causes are (1) “ geographical changes 
which at one time isolate a whole fauna and flora, at another time 
lead to their dispersal and intermixture with adjacent faunas and 
floras ;” and (2) the changes of climate which have occurred in 
writers on this subject. 
Three chapters are devoted to the influence of the glacial epoch 
