CHARACTERS OF SPECIES. SCULPTURE. 281 



deceptive : see them alive, and they look like drops of 

 burnished gold ; look at them in cabinets, and they appear 

 like different insects, entirely of a dull yellowish colour : 

 yet let these very specimens be plunged in warm water, 

 and, while the moisture continues, all their rich metallic 

 hues will revive, as if by magic. The colours of many 

 of the apterous insects, especially of the spiders, would 

 enable us to discriminate the species with much pre- 

 cision ; but unfortunately they are more evanescent than 

 those of any other insects, nor has any method been yet 

 discovered for preserving them. We are therefore 

 obliged, reluctantly, to seek for other means to define 

 the species. The same remark applies to a large pro- 

 portion of the crabs ; although they will exhibit, if well 

 preserved, some faint indication of their original hues. 

 Changes of colour, in individuals of the same species of 

 birds, will be effected by extreme age : the green plumage 

 of parrots changes to yellow ; and aged females of the 

 gallinaceous order are known to assume the plumage and 

 colours of the male bird. We know not whether this 

 circumstance has been observed in wild birds ; but many 

 instances of this change are upon record in the cases of 

 pheasants, fowls, and other domesticated species. 



(342.) Sculpture is the last distinction of species 

 which we shall here enumerate. This term compre- 

 hends all those various modes by which nature has 

 diversified the naked parts of birds, the elytra or ex- 

 ternal wings and other parts of insects, the scales of 

 reptiles and of fish, and the hard or testaceous covering 

 of molluscous animals. The bodies of quadrupeds and 

 birds, being covered either with hair or feathers, show 

 very little of this peculiarity : the horns of the ruminating 

 animals, however, present us with different kinds of sur- 

 faces, as shown in the rings and nodules upon them ; 

 these are greatly diversified, and almost invariably in- 

 dicate a difference in species. Sculpture, in birds, is 

 restricted to grooves upon the bill of certain species 

 of hornbills and toucans ; and to the form, and mode 

 of division, of the scales on the feet. These latter 



