186 ORIGINAL ARTICLES. 



which must be taken as a guide in any attempt to frame a natural clas- 

 sification of that group, but as having an important bearing upon some 

 of those higher questions relating to the origin and value of differential 

 characters generally, which have recently been brought prominently 

 under consideration. In so doing, it is my desire to confine myself 

 purely to the scientific and practical aspect of these questions ; seeking 

 in the first place to determine, on the legitimate basis of induction, 

 what general principles may be educed from the comparison of the large 

 body of facts which I have brought together as regards the classification 

 of Foraminifera ; and then briefly inquiring how far the results of simi- 

 lar comparisons, made upon other types of organized structure, justify 

 the extension of the same principles to the Animal and Vegetable King- 

 doms at large. 



It may be well for me to advert in limine to certain peculiar features 

 in this inquiry, that render the group to which it relates singularly 

 adapted for a comparison at once minute and comprehensive amongst a 

 wide range of individual forms. The size of the greater part of these 

 organisms is so small, that many hundreds, thousands, or even tens of 

 thousands of them, may be contained in a pill-box ; and yet it is usually 

 not too minute to prevent the practised observer from distinguishing the 

 most important peculiarities of each individual by a hand-magnifier 

 alone, or from dealing with it separately by a very simple kind of mani- 

 pulation. Hence the systematist can easily select and arrange in series 

 such of his specimens as display sufficient mutual conformity, whilst he 

 sets apart such as are transitional or osculant ; and an extensive range 

 of varieties may thus be displayed within so small a compass, that the 

 most divergent and the connecting forms are all recognizable nearly in 

 the same glance. I am not acquainted with any other group of natural 

 objects in which such ready comparison of great numbers of individuals 

 can be made ; and I am much mistaken if there be a single species of 

 plant or animal, of which the range of variations has been studied by 

 the collocation and comparison under one survey of so large an assem- 

 blage of specimens as have passed under review in the course of these 

 investigations. 



The general fact which I desire to bring prominently forward as the 

 result of my investigations into this group, is, that in all the types pos- 

 sessing a wide geographical distribution which have been specially 

 studied by myself, or by others, the range of variation has also been 

 very wide ; so that not only what have been considered as specific, but 

 such as have been regarded as generic, and in some cases even as ordinal 

 differences, present themselves among organisms, which, from the inti- 

 macy of the mutual relationship that is evinced by the gradational cha- 

 racter of those differences, as well as by the variation presented in the 

 several parts of one and the same organism, must in all probability have 

 had a common origin.* 



* I have the authority of M. Deshayes for the belief that the excessive multiplication 

 of generic and specific distinctions, which so greatly impairs the value of the late M. 



