HABITS OF ANIMALS. 87 



the distinction of species. Some of the most perplexing 

 questions in Zoology and Palaeontology might long ago 

 have been settled, had we had more precise information 

 upon this point, and were it better known, how unequal 

 in this respect different groups of the animal kingdom are, 

 when compared with one another. While the individuals 

 of some species seem all different, and might be described 

 as different species, if seen isolated, or obtained from dif- 

 ferent regions, those of other species appear as if all cast 

 in one and the same mould. It must be, therefore, at once 

 obvious, how different the results of the comparison of 

 one fauna with another may be, if the species of one have 

 been studied accurately, for a long period, by resident 

 naturalists, and the other is known only from specimens 

 collected by chance travellers ; or, if the fossil representa- 

 tives of one period are compared with living animals, 

 without both faunas having first been revised according 

 to the same standard. 1 



Another deficiency, in most works relating to the habits 

 of animals, consists in the absence of general views and of 

 comparisons. We do not learn from them, how far ani- 

 mals related by their structure are similar in their habits, 

 and how far these habits are the expression of their struc- 

 ture. Every species is described as if it stood alone in 

 the world ; and its peculiarities are mostly exaggerated, 

 as if to contrast more forcibly with all others. Yet, how 



1 In this respect I would remark should be altogether rejected in the 



that most of the cases in which spe- investigation of general questions in- 



cific identity has been affirmed be- volviug fundamental principles, as 



tween living and fossil species, or untrustworthy observations always 



between the fossils of different geolo- are in other departments of science, 



gical periods, belong to families which Compare further my paper upon The 



present either great similarity or ex- Primitive Diversity and number of 



traordiuary variability, and in which animals, quoted above, page 35, 



the limits of species are therefore in which this point is specially consi- 



very difficult to establish. Such cases dered. 



