440 SUMMARY OF CURRENT RESEARCHES RELATING TO 



it to be hypodcnnal, Avliilc the outer chitiu-sliell, or covering of the 

 head, resists all bleaching action, remaining green until it is macerated. 



" I cannot yet wholly understand why the scales of Lepidoptcra 

 divschargc the air contained in them so much more readily, when sub- 

 jected to trcatni'^nt with alcohol and chloroform, than do the scales of 

 Coleoptcra, while, on the other hand, water will drive out the air from 

 scales of Coleoptera much quicker than from scales of Lepidoptcra. 

 There are several things which might cause these phenomena, but I 

 am inclined to the opinion, without having p-oved its conectncss, that 

 their cause is the presence of more oil in the scales of Lepidoptcra than 

 in those of Coleoptera. This would coincide with the greater lustre of 

 lcj)id()ptorous scales, and with other points in their ai^iiearance. Per- 

 haps the entrance of the shauk of the scale is only closed with an 

 oily mass, for I have never seen the scale of a lepidopteron resist 

 entirely the entrance of fluid, as is often the case with the scales of 

 Coleojitera. 



" The stria3 upon scales of Lepidoptcra have long been a subject of 

 investigation, but, as far as I know, no one, up to 1880, published the 

 fact that their strijc were upon the outside, or upon the side turned 

 aw\ay from the wing. In Burgess's paper on Danais * in that year he 

 figures transverse sections of the scales of that butterfly, and calls 

 attention to tlie fact. Without having seen Burgess's i)aper, in the fol- 

 lowing year I noticed that the stria> upon the scales of the proboscis 

 of Culcx were on the outside, and so figured them in my dissertation | 

 and in ' Psyche.' % By the transverse section of a scale of Alans, 

 figured in this paper, it will be pcen that there too the strife are ujjon 

 the oiater surface. That I have found to be the case with the principal 

 or external strias, in all beetle-scales which I have examined. It is, 

 briefly expressed, only the development of a mechanical law, which 

 extends to many surfaces which shrink by drying or cockling. It can 

 be easily illustrated by partly filling a bladder with water and allow- 

 ing it to dry upon a board. The main folds will be, of course, upon 

 the exposed upper side, and the longitudinal ones will be the more 

 prominent. 



" Another easy way to prove that the strife upon the scales of the 

 wings of Le^ndoptera are upon the side away from the wing is to take 

 impressions of the scales upon a surface of collodion. These imjires- 

 sions are readily taken by pressing quite lightly a dry butterfly's 

 wing upon a microscojie slide, which has been moistened with a solu- 

 tion of collodion in ether. The wing should be removed before the 

 collodion has become thoroughly dry, when beautiful impressions of 

 the outer surface of the scales will remain on the collodion surface, 

 and may be mounted for future study. A very little practice will 

 enable one to remove the wing at the proper moment ; if left too long 

 the greater part of the scales will be removed from the wing and 

 adhere to the collodion. In order to take impressions of the under 

 sides of scales, the latter should be transferred by a process described 



* Anniv. Mem. Bost. Soc Nat. Hist.. 1880. 



t Dissertation, Leipzig University, 1881, pi. 1, figs. 8, 12-15. 



t Psyche, July-Sept , 1881. 



