TRANSACTIONS OF THE SECTIONS. 103 



He thought it probable that a great deal of the obscurity in which this subject 

 is involved arose from our inadequate ideas with respect to the degree to which cer- 

 tain species may vary, without losing their identity, and the unwillingness of some 

 naturalists who have been long accustomed to other ways of thinking, to receive the 

 facts as conclusive, which have been adduced in support of this opinion. He then 

 adverted to certain facts and observations which had been brought forward of late 

 years by different naturalists to show the variation to which many species are liable 

 in the classes of Insects, Birds, and Shells. Several conclusions arrived at by Mr. 

 Wollaston*, in reference more especially to the coleopterous insects of the island of 

 Madeira, were much dwelt upon. Variations of structure, size and colouring had 

 been found by that gentleman to be often connected with the insular or continental 

 stations in which these insects lived, the temperature of the climate, the altitudes at 

 which they were found, and their greater or less proximity to the sea. 



In the class of Birds, a few cases were alluded to in which the adult males of cer- 

 tain species in certain countries appeared never to arrive at the same state of plumage 

 which characterized the very old male in others : also the instance of the common 

 Ruff {Machetes pugnax) , which, according to Mr. Blythef, is never met with in the 

 neighbourhood of Calcutta in the breeding plumage, by which it is so remarkably 

 distinguished in Europe. Mention was then made of several common European 

 birds, of which two or more races existed in different parts of the continent, each 

 characterized by certain constant peculiarities of plumage, and which it was very 

 desirable should be studied more closely, especially in respect of habits and manner 

 of life, by those who had the opportunity, in order to ascertain whether they have 

 any real claim to be elevated to the rank of species, the light in which they have 

 been considered by some naturalists : — such, for example, as the Sylvia suecica of 

 Latham, of which one race exists in the north of Europe having the pectoral spot 

 rufous, and another in the central and south parts having the same spot white ; the 

 Saxicola aurita, and the S. stapazina, found, at least in the greatest plenty, in the 

 north and south parts of Italy respectively, and only to be distinguished by the 

 colour of the throat ; the Common, Cisalpine, and Spanish Sparrows, the differences 

 between which, and those very slight, were almost confined to the adult males ; the 

 many so-called species of White and Yellow Wagtails, mostly inhabiting different 

 parts of Europe, though occurring, some of them, together in some places. It was 

 observed, in reference to these and similar cases, that if two closely-allied species 

 are found living together always, without any individuals occurring of an intermediate 

 kind, it is a strong argument for their being really distinct. But if they are mostly 

 found in two different countries or districts, the same inference cannot be drawn from 

 the circumstance of their being occasionally met with together in the localities lying 

 between those two countries, or bordering on them when contiguous. 



In the above-mentioned instances, the differences between the supposed species 

 rest principally in the plumage j but the author went on to speak of others, in which 

 these are combined with slight differences of foim or size of parts, but on which it 

 was shown, from many recorded observations, no greater reliance could be placed, 

 as a ground at least in all cases, of specific distinctness. The differences between 

 the White-winged Cross-bills of America and Europe, as indicated by De Selys- 

 Longchamps+, were adduced as a probable example of this kind of variation. That 

 naturalist observes that these two Cross-bills (which have been considered by some 

 naturalists as two species to which the names of Loueia leucoptera and L. bifasciata 

 have been respectively given) differ slightly, but constantly, in size, form of the bill, 

 depth of the red tint of the plumage, and proportions of the wings and tail. He 

 thinks, nevertheless, that these are only the distinguishing marks of two races, sprung 

 originally from the same stock, — one race having fixed itself in the North of America, 

 the other in the North of Asia. He suggests, in explanation of the modified form of 

 the bill in the two kinds, that, in birds which use the bill as pinchers for detaching 

 the seeds of fir-cones, and tearing them violently away, the shape of this organ may 

 to a certain extent be affected by the different forms of fructification in the different 



* In a little work ' On the Variation of Species,' 1855. 

 t Ann. and Mag. of Nat. Hist. vol. xii. p. 170. 



t " Notice sur les Becrois6s Leucoptere et Bifascie,'' Bull, de I'Acad. Roy. de Belg., 

 tom. xiii. 



