18 PHILOSOPHY OF ZOOLOGY, 



rich and vivid ; those of the winter obscure and dull. This 

 is well illustrated in the dunlin {Tr'inga alpina), whose 

 summer plumage is much intermixed with black and ru^ 

 fous colour, but whose winter plumage is dull and cine- 

 reous. In its winter dress it has been described as a dis- 

 tinct species, under the name of T. cinclus, or Purre. Si- 

 milar instances mig4it be produced in the wagtails, lin- 

 nets, and plovers, and a great many other birds. 



The circumstances under which these changes are ob- 

 served to take place, indicate their dependence on tempera- 

 ture, as connected with the season. The deep colours of 

 the summer dress are exchanged for the lighter or whiter 

 colours of the winter, with a rapidity and extent propor- 

 tional to the chanoes of the seasons. During; a mild autumn, 

 the shifting of the dark for the light coloured dress proceeds 

 at a very slow pace ; and when the winter also continues 

 mild, the white dress is never fully assumed. In some 

 species, as the black guillemot, the white winter dress is 

 never acquired in this chmate, although its ash-coloured 

 plumage intimates a tendency to the change. In the cli- 

 mate of Greenland, on the other hand, the change is com- 

 plete, and the plumage is of a sno^vy whiteness ; as we had 

 an opportunity of observing in the collection of the Dublin 

 Society in 1816, in a specimen in its winter dress, brought 

 from Greenland by an intelligent and enterprising natural- 

 ist, Sir Charles Giesecke'. 



Having thus seen that the colour of the clothing of many 

 animals changes with the season, and that, however diver- 

 sified the summer dress may be, the coloiu* during winter 

 approaches to white, it may now be asked. What benefit is 

 derived from this arrangement * ? 



* Some species of gulls exhibit in their winter plumage very striking de- 

 viations from this general rule. Montagu, in his Supplement to the Orni- 



