23 PHILOSOPHY OF ZOOLOGY. 



The moulting of birds takes place in all cases gradually, 

 and in those species whose plumage changes colour with 

 the reason, the different moultings take place at corre- 

 sponding periods. In the autumn, we find that the black 

 feathers on the head of the Lams ridibundus change to a 

 white colour. But besides the altered feathers, others 

 spring up, of a white colour, to increase the quantity of 

 clothing. This gull has, therefore, during the winter, 

 some of the feathers of the head old, and others young. 

 Again, in spring the white feathers of the winter become 

 black, and a few new feathers make their appearance, like- 

 wise of a black colour, to supply the place of the older 

 ones which drop off in succession. Some of the feathers 

 on the head of this gull are half a year older than others ; 

 and consequently, we may infer, will fall off sooner than 

 those of more recent growth. From these, and similar 

 facts, furnished by several species of British birds, we are 

 disposed to conclude, that the feathers which are produ- 

 ced in autumn and the beginning of winter, and which 

 correspond with the conditions of the season, change 

 their colour in spring, and continue in this state until 

 they are shed in autumn. The feathers which are pro- 

 duced in spring, continue of the same hue during the 

 summer, change their colour in winter, and fall off again 

 s upon the approach of spring. In this manner, the quanti- 

 ty of the plumage fit for the different seasons of the year 

 is easily regulated, and it is only necessary that the change 

 of colour in each feather should take place but once in the 

 course of its connection with the bird. By these arrange- 

 ments, the welfare of the individual is promoted by the 

 simplest means. 



Many animals, Avhich are unable to provide against the 

 vicissitudes of the seasons, by varying the quantity and the 

 colour of their dress, are, ncvertlielcss, protected by being 



