64 J. WATSON ON CERTAIN SCALES 



which they are attached to the membrane of the wings. 

 These scales are flat, like those of fish, and show striated 

 markings. Referring to them in his ' Introduction to the 

 Classification of Insects/ Westwood says, '^ Lyonnet has 

 filled several quarto plates with representations of these 

 scales, varying to almost every form, taken from the wings 

 and body of the Goat Moth ; so that the suggestion of a 

 writer, that the forms of these scales might be used for 

 specific characters, is entitled to no weight." (He likewise 

 refers to a paper upon the same subject by a French author, 

 presently to be noticed.) But at the time this was written 

 the microscope showed all the scales as nearly flat ; and now 

 the binocular instrument enables observers to discover 

 rotundity where it was not previously suspected. By help 

 of the above instrument it appears probable that two or 

 more different kinds of scales, serving distinct and separate 

 offices, are to be found in lepidopterous insects ; and this 

 difference of function has not hitherto been suggested. 



In some genera of the diurnal Lepidoptera, besides the 

 ordinary scales, some peculiar forms exist; and it is to 

 these attention is now to be drawn, especially to those 

 found in the genus Pieris and its congeners. Examination 

 with the binocular microscope shows that these scales are 

 not flat like the others, but cylindrical and hollow ; they 

 are attached to the wings by a bulb, at the end of a thin 

 elastic peduncle differing in length in different species. The 

 bulb also varies in size and shape ; and there is a hole or in- 

 dentation to receive it in the membrane of the wing, larger 

 than that for the ordinary scale ; and the whole apparatus 

 has the appearance of a ball-and-socket joint, allowing con- 

 siderable facility for motion or play. The scales are fixed 

 to the wings at the broader instead of the narrower ex- 

 tremity, and there they are furnished with a fringe of 

 cilia or hairs. The scales are placed on the upper surface 

 of the wings, principally on the superior ones, with their 



