AFFINITIES CONNECTING ORGANIC BEINGS 471 



be natural; for, on the principle of inheritance, all the forms 

 descended, for instance, from A, would have something in 

 common. In a tree we can distinguish this or that branch, 

 though at the actual fork the two unite and blend together. 

 We could not, as I have said, define the several groups ; but 

 we could pick out types, or forms, representing most of the 

 characters of each group, whether large or small, and thus 

 give a general idea of the value of the differences between 

 them. This is what we should be driven to, if we were ever 

 to succeed in collecting all the forms in any one class which 

 have lived throughout all time and space. Assuredly we shall 

 never succeed in making so perfect a collection : nevertheless, 

 in certain classes, we are tending towards this end ; and 

 Milne Edwards has lately insisted, in an able paper, on the 

 high importance of looking to types, whether or not we can 

 separate and define the groups to which such types belong. 

 Finally, we have seen that natural selection, which follows 

 from the struggle for existence, and which almost inevitably 

 leads to extinction and divergence of character in the de- 

 scendants from any one parent-species, explains that great 

 and universal feature in the affinities of all organic beings, 

 namely, their subordination in group under group. We use 

 the element of descent in classing the individuals of both 

 sexes and of all ages under one species, although they may 

 have but few characters in common ; we use descent in class- 

 ing acknowledged varieties, however different they may be 

 from their parents; and I believe that this element of descent 

 is the hidden bond of connexion which naturalists have 

 sought under the term of the Natural System. On this idea 

 of the natural system being, in so far as it is has been per- 

 fected, genealogical in its arrangement, with the grades of 

 difference expressed by the terms genera, families, orders, 

 &c., we can understand the rules which we are compelled to 

 follow in our classification. We can understand why we value 

 certain resemblances far more than others ; why we use rudi- 

 mentary and useless organs, or others of trifling physio- 

 logical importance ; why, in finding the relations between one 

 group and another, we summarily reject analogical or adap- 

 tive characters, and yet use these same characters within the 

 limits of the same group. We can clearly see how it is that 



