﻿182 THE ENTOMOLOGIST. 



reagents on the colours might well be a function, partly, of the 

 duration of action. After a few preliminary trials, I determined 

 to leave the colours under the action of the reagents for one hour, 

 in every case. (I may add, however, that in all the cases where 

 the most striking results were obtained, the action was very rapid, 

 or often instantaneous ; nevertheless, the time effect was apparent 

 in many cases, and, anyhow, the safeguard was there.) 



The various colours required were cut out from the wing, 

 placed in watch-glasses and covered by the reagent, being left 

 thus exposed — as already stated — for one hour. But at the very 

 outset I was encountered by a difficulty here : " Like water off a 

 duck's back" is an ancient proverb, and exactly describes the 

 way in which the liquids gathered up in spherules and rolled off 

 the scaled wings ; in fact it was impossible to wet these ; and it 

 immediately struck me how very stupid I had been in not 

 expecting this certain result. The question then arose, how to 

 overcome this difficulty. One obvious solution was to first touch 

 the wing with alcohol, which of course soaks it thoroughly, and 

 so enables watery solutions to wet it ; but I was unwilling to use 

 alcohol, except as a last resort; (for that would necessitate a 

 complete set of blank experiments with alcohol alone ; and 

 should it be found of itself to act in any cases, the problem 

 would become complicated). After a little consideration, I deter- 

 mined to try gumming the bits of wings on to a watch-glass. 

 This answered admirably, — at least when I left them some hours 

 to dry in ; but if the reagents be applied too soon, some of the 

 wings become detached, and swim about half-dry on the surface 

 in the most intolerably exacerbating manner; — a "superfluity 

 of naughtiness " on their part scarcely conducive to sweetness of 

 temper on the experimenter's. 



It will be understood, then, that these wings were not merely 

 wetted by the various reagents and then left, but were actually 

 submerged in the reagent for one hour. 



Recording the results. — Here I encountered another difficulty ; 

 one, too, which cannot be said to have been really overcome at 

 all, — and this is the want of a colour standard. The natural 

 colours of the wing are themselves not always easy to describe 

 accurately and uniformly ; some, of course, may be disposed of 

 at once, as blue, yellow, green, and so on ; but in very many cases 

 it is very difficult to decide whether a colour shall be designated 

 yellow or orange ; brown, chestnut, or chocolate ; and so on. As 

 concerns this, however, I have been to great extent guided by the 

 results, and — as will be seen — have not scrupled to divide certain 

 colours (in what may at first sight seem a somewhat arbitrary 

 manner) from certain others that look almost identical, but really 

 are found to have a different constitution. As an example, I may 

 refer to tabulations to be given hereafter, where the colours of 



