ORQANIG BEINOa. 449 



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 toward this end; and Milne Ed- 

 wards 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 fol- 

 lows from the struggle 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 or- 

 ganic beings, namely, their subordination in group under 

 group. We use the element of descent in classing the 

 mdividuals 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 con- 

 nection 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, etc., we can under- 

 stand the rules which we are compelled to follow in 

 our classification. We can understand why we value 

 certain resemblances far more than others ; why wc 

 use rudimentary and useless organs, or others of trifling 

 physiological importance; why, in finding the relations 

 between one group and another, we summarily reject ana- 

 logical or adaptive characters, and yet use these same char- 

 acters within the limits of the same group. AVe 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. Wo 

 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. 



