282 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 



characters^ however, are found so uniformly prevalent 

 through the species of a natural group, that they are 

 mostly employed in defining genera and sub-genera : 

 slight alterations from such standards nevertheless occur 

 in species ; and they consequently claim the especial 

 attention of the ornithologist. That he may be con- 

 vinced of this, let him compare the form, size, and 

 manner of disposition of the scales upon the feet of a 

 few different groups ; as, for example, a crow, shrike, 

 chatterer, and flycatcher ; and he will at once perceive 

 how singularly they are diversified. So, likewise, are the 

 scales of reptiles and of fish. On proceeding to insects, 

 we find this character rising in importance, particularly 

 in the coleopterous order. Sometimes the wing-cases 

 are punctured, either irregularly or in lines ; in others, 

 they are either grooved, ribbed, wrinkled, spined, or 

 tuberculated : and each of these are again diversified in 

 " an almost infinity of ways. Better distinctions for 

 species than these, cannot possibly be obtained ; and they 

 accordingly are used for this purpose by the best 

 writers. The same diversity may be observed both among 

 the univalve and the bivalve shells ; the surface of which 

 are diversified — according to the species — either 

 with spines, nodules, tubercles, wrinkles, grooves, 

 ridges, simple lines, or punctured lines ; and sometimes 

 these lines cross each other like the fabric of a basket, 

 and they are then termed cancellated. The sculpture 

 of corals, and of the spines upon the different sea eggs 

 {Echini), afford excellent specific distinctions, and may 

 always be so employed. Lastly, we may notice, under 

 this head, that partial clothing on the surface of many 

 animals, otherwise naked, which is termed pubescence. 

 This is chiefly confined to insects ; and consists of downy 

 hairs, of different degrees of density and length, spread 

 either wholly or partially over their body. The highest 

 developement of this is seen in the field bees {Bombus) ; 

 but it is very prevalent among beetles, particularly such 

 as represent, in their different circles, the order of 

 Hymenoptera. This pubescence is either partial or 



