PRINCIPLES OF SCIENTIFIC ARRANGEMENT. 123 



cific form in the succession of generations, that even 

 the shadow of a deviation from the typical distinction is 

 scarcely to be discovered : a reason for this it is hard to 

 surmise. We may, nevertheless, conclude it to be cer- 

 tain that true species are ever distinct, and can no more 

 coalesce, however closely they may approach together, 

 than can asymptotes. 



Specific differences result from many characteristics, 

 from colour, clothing, size, and sometimes from pecu- 

 liarities of structure; but these last are usually of a 

 higher order, tending to indicate an aberration, slight 

 though it be, from the normal generic character which 

 holds the group together, thus implying a distinctive 

 economy. This is sometimes called a subgeneric attri- 

 bute, and there might be a reason, certainly, for not 

 elevating such species to the full rank of genera, were 

 genera equivalents, which they are not, and it merely 

 remains an evasive admission of the doubt that attaches, 

 except for the sake of convenience, to any subdivision, 

 but the specific. 



The species is thus the very last term of subdivision, 

 the very elemental principle itself, which unites toge- 

 ther as one, solely for the purposes of perpetuation, the 

 two sexes of similar individuals, and without whose in- 

 tercourse the kind or species would die out. 



That some species greatly abound in individuals, as 

 before observed, whilst others appear to be extremely 

 limited, is an absolute fact, and not merely suggested 

 by a defective observation of their occurrence, resulting 

 from their rapid dispersion. It is verified by being 

 noticed to occur where we know they would resort, as is 

 exemplified in the case of some of the parasitical species 

 of the insects herein treated of, and which are sometimes 



