392 ORDERS OF PTILOTA. 



or nerves, as they have been called, but which Dr. Leach 

 termed Pterygostia or udng- bones. These nerves here, as in 

 the Diptera and Hymenoptera, according to their number 

 and position^ offer very important characters for generic dis- 

 tribution, but virhich have been too much neglected by 

 authors. M. Boisduval, hov^ever, in his just published 

 Species General des Lepidopteres, Paris, 1 836, has performed 

 good service in this branch of the science by describing and 

 delineating the nerves of the wings of many of the species of 

 Lepidoptera : although it is proper to observe, in justice to 

 our own countryman, Jones, that he long ago published a 

 valuable memon- in the second volume of the Linnaean 

 Transactions, in which the same subject was well treated. 

 The structure of the scales, which give to the wings of these 

 insects all their beauty, has been already described. The 

 slight manner by which they are attached to the wing causes 

 them to scale off on the least touch, so that by laying a 

 butterfly in a reversed position on a piece of gummed paper, 

 an exact impression of its markings will be obtained ; the 

 scales, however, being reversed, the broad extremity of 

 each series of scales which was laid ( roof-like ) upon 

 the succeeding row, being hidden, and the pointed 

 base exposed. In some species the representation will 

 not resemble the markings of the butterfly, evidently 

 owing to these species having a double la3^er of scales on 

 both sides of the wing, the under layer usually consisting of 

 white scales. On denuding a wing of its scales, the points 

 in which they were inserted are clearly to be perceived in the 

 form of minute dots. Of the number of these scales it would 

 be difficult to give a correct idea in the various species. 

 Leuwenhoeck, however, states that there are more than 

 400^000 on the wings of the moth of the silk-worm. In 

 some species of Lepidoptera, however, the wings are more or 

 less vitreous, and consequently denuded of scales, or have 



