Chap. XIV.] AFFINITIES CONNECTING ORGANIC BEINGS. 381 



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 straggle for existence, and which almost inevitably leads to 

 extinction and divergence of character in the descendants 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 classing 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 has been perfected, 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 rudimentary and useless organs, or others of 

 trifling physiological importance ; why, in finding the relations 

 between one group and another, we summarily reject analogical or 

 adaptive characters, and yet use these same characters within the 

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

 living and extinct forms can be grouped together within a few great 

 classes ; and how the several members of each class are connected 

 together by the most complex and radiating lines of affinities. We 

 shall never, probably, disentangle the inextricable web of the 

 affinities between the members of any one class ; but when we have 

 a distinct object in view, and do not look to some unknown plan of 

 creation, we may hope to make sure but slow progress. 



Professor Hackel in his ' Generelle Morphologie ' and in other 

 works, has recently brought his great knowledge and abilities to bear 

 en what he calls phytogeny, or the lines of descent of all organic 

 beings. In drawing up the several series he trusts chiefly to 

 embryological characters, but receives aid from homologous and 

 rudimentary organs, as well as from the successive periods at which 

 the various forms of life are believed to have first appeared in our 

 geological formations. He has thus boldly made a great beginning, 

 and shows us how classification will in the future be treated. 



