342 
OX SPECIFIC DISTINCTIONS. 
together. This is a very definite character, and which is subject to no divarica¬ 
tion.” If the Doctor’s position admitted of no divarication (which it does and 
greatly so), it could benefit us little, as the information necessary for the applica¬ 
tion of the test is, in the vast majority of cases, entirely deficient. 
To pass on to the opinion given above, viz., that if two presumed species are 
so connected, together by intermediate varieties, That not a single perpetual and 
invariable (however slight) distinction can be discovered , they must be considered 
identical. As the habits of many species have not been observed, and others 
present no difference whatever in this respect, the general marks of distinction 
are taken from the structure , colour , and size. 
As examples of closely-approximating yet distinct species , I shall select some of 
those given in Mr. Blyth’s excellent paper on the Mealy Linnet (Vol. II., p. 453). 
Thus, for instance, we find that Elanus melanopterus (African species) and E. 
dispar (American sp.) approach each other so closely in size and colour as to be 
indistinguishable in these respects; but the former has the outer feather of the 
tail rather the longest, which in the latter species is more than half an inch 
shorter than the next. This peculiarity in the structure is always present. The 
Bullfinch ( Pyrrhula modularis ; P. vulgaris , Auc.) is represented in Japan by a 
species from which it differs very slightly but permanently in the colour of a single 
feather. Almost as slight, though quite as invariable a peculiarity of colour 
forms the only point of distinction between Budytes flava and B. neglecta ( B. 
cyanocephala, N. Wood) ; Motacilla alba, Linn., and M, maculosa, (M.Yarrellii , 
Gould) ; Garrulus glandarius, and the allied Jays of Asia-Minor and Japan ; 
and between numerous others. Then again, Pyrrhula modularis , which agrees 
exactly in all points of colour and structure with the Great Bullfinch, is yet 
distinguishable by an invariable inferiority in size. In all the above instances— 
and numerous similar ones might readily be added—it will be noticed that there 
exists, notwithstanding an approximation even to entire similarity in other 
respects, some peculiarity which is invariably present in one species, and absent 
in the others; and the importance of which as a distinctive character is 
never destroyed by intermediate modifications. Consequently we find that such 
species are classed as distinct; and in many cases a diversity of habits, &c., fully 
warranting their being considered genuine species, has been observed. 
On the contrary, let us examine one or two forms in which no single distinctive 
character is preserved through their various modifications. Take, for instance, 
Pontia chariclea of Stephens. The claims of this insect to rank as a species 
must, as in the preceding examples, be furnished by its structure, colour, or size. 
In the first particular it is exactly similar to P. brassicce, and the differences 
observable in its colour and size are entirely lost in the intermediate varieties. 
It does not , in fact, possess one constant distinctive char oxter istic. The same 
