1889.] 



THE YOUNG NATURALIST. 



agestis. This species, which resembles the Lycanida in its transforma- 

 tions, is quite destitute of the characteristic " battledoor " scales. 



The males of many butterflies have scales peculiar to the sex ; thus 

 the tufted scales of Satyrus megcera, Anthocharis cardamines, Piens napi, P. 

 rapa (Fig. 13), P. cvatcegi and Argynnis paphia, characterize the one sex 

 only. But not only has the upperside of the wings the exclusive posses- 

 sion of certain peculiarly formed scales, but the underside likewise lays 

 claim, in many instances, to sole right of ownership. A single example 

 will suffice, that being the pretty little Green Hairstreak butterfly 

 (Thecla rubi.) Mingled with the ordinary typical form will be found a 

 numerous sprinkling of rudder-like scales, which look exactly as 

 though a good third part had been cut off them, leaving the remaining 

 two-thirds with the usual peduncle and its axial continuation at one 

 side. Fig. 14, which represents this scale as viewed with a quarter 

 inch objective, does not show the granulations composing the parallel 

 striae : a higher power lens is necessary to bring out these markings 

 with clearness. 



It is the middle layer of membrane that originates the brilliance 

 of colour emitted by many scales, and its reflective power is only 

 minimised by a preponderance of dark colouring granules in the outer 

 laminae. Perfectly colourless scales give to the wing of an insect a 

 metallic lustre, and in such instances, Plusia chrysitis and P. festuca for 

 example, two striated layers only are present. White scales, however, 

 as I have already had occasion to observe, owe their appearance to 

 colourless granulations, which act upon rays of light much in the same 

 manner as pulverized glass. 



As we approach the marginal fringes of the wings, the scales become 

 more and more elongated, while the dentations upon the free ends 

 increase in size in a corresponding ratio. Even the transition of scales 

 to hairs becomes easy and natural. 



The Trichoptem, which includes the well-known caddice flies, needs 

 but small comment. Their wings are ample and well-developed, 

 sometimes very thickly clothed with hair, the posterior pair being 

 longitudinally folded when the insect is at rest. Yet, notwithstand- 

 ing the large expanse of wing, the caddice flies are nevertheless clumsy 

 flyers, but as they chiefly pass their life in a limited locality, we would 

 not be led to expect exceptional powers of flight. Moreover, from 

 the extremely rudimental formation of the mouth, it is probable that 

 the procuration of nourishment is rendered unnecessary, and long 

 foraging excursions therefore needless. 



