82 INTRODUCTION. 



of some shade of earthy-brown, or of greyish sand 

 colour ; this is broken by dots and blotches, either 

 light or dark, blackish or reddish, but always so 

 disposed as to resemble those under shades, as they 

 may be called, which are caused by the inequalities 

 of the ground, and the presence of particles of dif- 

 ferent tints that may be upon it. Thus, whether 

 we contemplate the God of Nature in his more 

 sublime productions, or in those provisions which he 

 makes for the well-being of his humblest creatures, 

 the same principle of design, the same perfection in 

 execution, is equally conspicuous." (i. 313.) 



In the instances hitherto referred to, it will be 

 observed that the changes appear to be speedily 

 produced, and rapidly altered again ; and this solely 

 through the agency of different shades of light. 

 It must not, however, be supposed, that these 

 form the only circumstances in which change of 

 colour presents itself. Mr. Yarrell states, that he 

 had obtained a variety of Perch from ponds in 

 Yorkshire, which, when received, were of a uni- 

 form slate-grey colour, with a silvery tint ; and 

 this peculiarity of tint was retained when the living 

 fish are transferred from the park-ponds to other 

 waters, (i. 5.) " In certain waters," says Mr. Grif- 

 fith, " the shades of the Pike sometimes vary, and 

 it becomes yellow, with black spots ; according to 

 Sch wenckf eld, some are perfectly white." (Griff. 

 Cuv., x. 465.) Once more, Sir Humphry Davy, 

 " I lave known fish trouts from some lakes 

 '.n I; land, mottled in a most singular way, their 



