Chap. II. GENERAL REMARKS. 11 



investigations to the structure of special classes, either considering them by them- 

 selves or comparing them with allied types. Others still, look upon structure chiefly 

 with a view of ascertaining the functions of the organs, and may trace these 

 functions either through the whole series of animals or within the limits of some 

 particular group. The danger of this kind of researches lies in the tendeucj^, forced 

 upon the investigator at almost every step of his inquiry, to take the functions 

 as a safe guide in the appreciation of the true structural character of the organs. 

 On the other hand, the student of microscopic anatomy traces chiefly the elementary 

 parts of all the organic structures; but while he reveals to us a world unseen 

 by the ordinary powers of our senses, he is apt to overlook the more compre- 

 hensive relations of all these parts in their extensive combinations. The same may 

 be said of the embryologists. They confine their studies too exclusively to the 

 investigation of the earlier periods in the development of animals, and leave gener- 

 ally unnoticed that state of growth during which the new being, having acquired 

 an unmistakable resemblance to its parent, has still to go through a series of 

 transformations before it is itself capable of reproducing its kind. Moreover, during 

 these changes most animals have very different forms, and display sometimes so 

 striking a resemljlance to full-grown animals of other types, that these analogies 

 ought to be traced more closely than is usually done. Finally, palaBontologists have 

 of late become so thoroughly satisfied that the animals of past ages are entirely 

 diiferent from those now living, that they too frequently proceed to describe extinct 

 species without due comparisons with the living ones; and even represent fossil 

 remains as distinct species, without first determining how far species may be dis- 

 tinguished by the parts they have on hand. It is now, indeed, one of the most 

 pressing desiderata for the palaeontologists to ascertain what are the parts in different 

 classes of animals which may l^e sufficient to identify a fossil genus, and what is 

 further required to determine the species. When I see how many fossil fishes have 

 been described within the last fifteen years as distinct from those now in existence, 

 without allusion to any comparisons with the skeletons of their living representatives, 

 I think it may well be asked whether it was done with a full consciousness ot 

 the limitation which the similarity of the skeleton of species of the same genus 

 forces upon the attempts of the palaeontologists. 



The study of organized beings, considered from these different points of view, 

 has necessarily led to the division of our science into a number of very distinct 

 branches, now mostly cultivated as specialities by different individuals ; and yet all 

 these different branches of Natural History are only the systematized results, as it 

 were, of one-sided considerations. A complete history of an animal should embrace 

 the whole in a proper coordination. Their separation is only the natural conse- 

 quence of the difficulties inherent in the investigations, and of the necessity of 



