PEOOFS OF ORGANISING AilXD 325 



only to the special case of the Lepidoptera, l)ocnu>c these are 

 far more popuLarly known, and the special feature which dis- 

 tinguishes them from most other insects is fauiiliar to every 

 one, and can be examined by means of a good pocket lens or 

 microscope of moderate power. I allude, of course, !<• the 

 •wonderful scales Avhich clothe the wings of most buttcrllics 

 and moths, and which produce the brilliant colours and in- 

 finitely varied patterns with which they are adorned. (){' 

 conrse, the still more extensive order of the C(deoptera 

 (beetles) present a similar phenomenon in the cuh^urs and 

 markings of their wing-cases or elytra, and what is said of 

 the one order will apply broadly to the other. 



The wings of butterflies can be detected in very young 

 caterpillars when they are only one-sixth of an inch long, as 

 small out-foldings of the inner skin, which remain unchanged 

 while the larva is growing; but at the chrysalis (or pupa) stage 

 the wings ex^iand to about sixty times their former area, and 

 the two layers of cells composing them then become visible. 

 At this time they are as transparent as glass ; but two ur three 

 weeks before emergence of the imago they become opaque white, 

 and a little later dull yellow' or drab; twenty-four hours later 

 the true colours begin to appear at the centre of each wing. 

 It is during the transparent stage that the scales begin tf> Ix* 

 formed as minute, bag-like sacks filled with protoplasm ; the 

 succeeding whiteness is caused by the protoplasm being with- 

 drawn and the sacks becoming filled with air. The pupal 

 blood then enters them, and from this the colouring matter is 

 secreted. The scales are formed in parallel lines along ridges 

 of the corrugated wing membrane. The more bfilliani enloui-s 

 seem to be produced from the dull yellow ]ugment by cheinical 

 chanc'es Avhich occur within the scales. A few davs belore 

 emergence the scales become fullv jxrown, as hii^hlv coniph.'X 

 structures formed of parallel rows of minute cells, each -cale 

 with a basal stem which enters a pocket of the skin or mem- 

 brane, which pockets send out root^ wlii(^h seem to penetrate 



