THEIR POSITION IN THE ANIMAL KINGDOM. 13 



this expression denotes nothing but the bare fact, 

 nothing but the mere statement, that in America 

 we do not meet with the camel but with the llama, 

 which in a few main characteristics shows some 

 affinity with it. The one * vicariates ' for the 

 other. Why ? we ask. What is the meaning of 

 such ' vicariating ' ? We get no answer. 



Now, in raising the study of zoology from the 

 stage of a mere descriptive method to the height 

 of a true science, we demand an explanation of 

 connections and agreements. Every endeavour 

 to comprehend the animal world, from a scientific 

 point of view, makes modern geology the basis of 

 its operations, and its testimony which is of fifty 

 years' standing is that the present condition 

 of the earth's surface, the distribution of land and 

 water, has proceeded from the most gradual and 

 primeval processes, except in cases of purely 

 locally interrupted transformations. Scientific 

 study must, secondly, accept the phenomenon of 

 the power of adaptability in organisms, that ver- 

 satility of the organs with which plants and 

 animals meet the variability of their external 

 circumstances, and adapt themselves to changes 

 that are taking place, by habit and by the gradual 

 changes of their own bodies which are connected 



