430 



the under jaw to the vertex of the head, just behind the orbit of the eye, in C. immutabilis, two 

 inches and one eighth ; C. olor two inches and a quarter. In C. immutabilis the bill is rather 

 more flattened, particularly in the middle, between the dertrum, or nail, and the nostrils ; the 

 protuberance at the base of the upper mandible is less developed. In the Polish Swan the 

 cranium is highest at the supraoccipital portion ; in the Mute Swan the cranium is highest at 

 the supraorbital portion ; but the greatest difference is perceptible on comparing the occipital 

 bones ; the upper portion of this bone in C. immutabilis protrudes considerably more, and there 

 are two oval foramina, one on each side, just above the foramen magnum, which are not present 

 in any specimens of C. olor that I have examined ; the portion forming the boundary of the 

 external orifice of the ear is much more prominent ; and the condyle forms a more acute angle 

 with the basilar portion of the occipital bone." 



There is no doubt that this Swan always differs from Cygnus olor in the young plumage in 

 being entirely or nearly white instead of brownish grey ; and though there are instances of broods 

 being mixed, some of the cygnets being white and others brownish grey, it seems probable that 

 these are the result of an alliance between a Mute and a Polish Swan. Besides the difference in 

 the form of the cranium given by Mr. Pelerin, the adult Cygnus immutabilis has a smaller berry, 

 a redder beak, a smaller eye, and smaller lamellae than Cygnus olor, and the young bird is not 

 only white instead of grey, but it has the beak pale purplish pink instead of plumbeous. I am 

 indebted to Mr. Eeeve, the well-known curator at the Norwich Museum, for a most interesting 

 series of coloured sketches of the heads of this Swan at various ages, taken by him from living 

 specimens in the possession of Mr. J. H. Gurney, to show the passage from the young to the 

 fully adult plumage. From these I have selected one of the young and one of the old birds for 

 my Plate. Mr. Gurney has kindly presented me with a specimen of the young Polish Swan 

 which has just assumed the full feather plumage, but has still remains of the down amongst its 

 feathers ; and this bird is white very slightly tinged with warm buff on the back. 



The Polish Swan, however, is not always so white in this state of plumage, as Mr. Southwell, 

 in a paper read before the Norfolk and Norwich Naturalists' Society on the 26th September 

 1876, gives some interesting details respecting young birds which were tinged with buff, which 

 I transcribe as follows: — "Since Mr. Stevenson's excellent monograph, which I have just read 

 ('The Polish Swan,' printed for private circulation), was written, I have had several additional 

 opportunities of examining Norfolk-killed specimens of the Polish Swan ; and other important 

 evidence has been accumulated, which tends greatly to strengthen my previous opinion, that the 

 so-called Cygnus immutabilis is really a true species. The Polish Swan has actually been bred 

 in confinement by Lord Lilford, producing white cygnets ; and from these white cygnets his 

 Lordship has again bred another generation of white cygnets. Lord Lilford does not appear to 

 have recorded this ; and it was only in the course of conversation that it came to light. Upon 

 being applied to by Mr. Stevenson, however, his Lordship kindly wrote him full particulars of 

 the occurrence, and at the same time expressed his decided opinion that the species is a good 

 one. Before, however, this was known, the Council of the Zoological Society, finding that the 

 pair in their possession mentioned by Mr. Stevenson did not breed in their confined home in the 

 Gardens, determined to intrust them to Mr. J. H. Gurney, hoping that more liberty and a change 

 of quarters might induce them to breed. In the spring of the present year they were accordingly 



