38 SOME THOUGHTS ON CLASSIFICATION 



difficulty which he cannot overcome, though he thinks he sees greater 

 difficulties in the opposite view. He conceives that certain tendencies 

 of development in respect to some parts of structure immutably 

 belong to the specific type, whilst others are modified by external 

 circumstances, but he cannot point out where the limit is placed or 

 reduce all the cases to a general law. He seems justified in pro- 

 nouncing the transmutation theory unproven, and, in some points of 

 view, unsatisfactory to the mind ; but he must confess himself unable 

 to give a plausible explanation of the known facts, according to the 

 common notion of creation of distinct species, and is therefore, unpre- 

 pared to meet his adversary with a rival theory. I cannot see that it 

 is reasonably required of the philosophical student of nature to trace 

 the forms he examines to their origin, excepting so far as he must 

 perceive them all to belong to a common plan, bearing the impress of 

 supreme power, wisdom, and benevolence, and if he is determined to 

 speculate not only on the present relations but the original production 

 of every known type, I believe he is as yet only at the beginning of 

 the difficulties he must encounter before he can grope his way into a 

 clear light. But not to pursue this subject at present I pass from 

 these preliminary considerations to offer some comments on what has 

 been done or attempted in respect to the natural grouping of organised 

 beings. 



The distribution of them all into two great kingdoms, as animals 

 and vegetables, was forced upon ignorant man even in his most savage 

 condition, and is admitted by all who have thought upon the subject ; 

 and yet to explain the real points of universal resemblance in the 

 members of each kingdom, and the differences which enable us most 

 certainly to distinguish the two, is by no means easy. Widely as the 

 most characteristic members of each kingdom differ from each other, 

 it is easy to point to organisms which have been referred sometimes to 

 one, sometimes to the other, by those who might be esteemed amongst 

 the best judges, and the final settlement of these doubts can hardly 

 yet be assumed — though individual naturalists may, in each case, have 

 satisfied their own minds. In truth this is but one case of a universal 

 law of organic nature, without due attention to which our attempts at 

 natural grouping will always fail, that there are plans of structure 

 consisting in the combination of various characters, all which charac- 

 ters are combined in the typical examples, whilst in different directions 

 there is a gradual fading out of each of them, and intermixture of 



