172 ZOOLOGICAL CAKDENS. 



Russia they take the place of" that which is improperly 

 termed the Tame species, submitting themselves with 

 equal readiness to the process of domestication. 



The external differences between these two Swans 

 are not at first sight very obvious ; but, trivial as they 

 appear, they are uniform and constant. The bill of 

 the present species is entirely destitute of protuberance 

 at its base, and its colours are in a great degree 

 reversed, the black occupying the point and nearly 

 the whole of the bill, its base alone and the spaces 

 extending from it beneath the eyes being of a bright 

 yellow. The legs are black or dusky; the iris brown; 

 and the entire plumage, as in the other species, pure 

 white, but with an occasional tinge of yellowish gray. 

 The young pass through similar gradations of colour 

 with those of the Tame Swan, and arrive, like them, at 

 their perfect plumage about the third or fourth year. 



Slight as are these outward differences, they are 

 fully sufficient for the detection of the species ; and the 

 separation founded upon them receives ample confir- 

 mation from anatomical characters of the highest im- 

 portance. Not to speak of the difference in the number 

 of their ribs, which are twelve in the Wild Swan, and 

 eleven only in the Tame, their tracheie or windpipes 

 afford unquestionable evidence of their distinctness. 

 This organ, which, in the Tame Swan, passes directly 

 from the Jieck into the cavity of the chest without 

 forming any previous convolution, enters in the Wild 

 species an appropriate cavity in the keel of the breast- 

 bone, within which it passes to a considerable depth, 

 then returns upwards, and is again inflected over the 

 edge of the sternum before plunging into the chest. 

 Ray was the first to point out this marked distinction 

 between the two birds, which had previously been 

 regarded as doubtful species. It was neglected, how- 



