XIV 



PROOFS OF ORGANISING MIND 301 



other enthusiastic workers ; but I will call attention here 

 only to the special case of the Lepidoptera, because these 

 are far more popularly known, and the special feature which 

 distinguishes them from most other insects is familiar to 

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

 lens or microscope of moderate power. I allude, of course, 

 to the wonderful scales which clothe the wings of most 

 butterflies and moths, and which produce the brilliant 

 colours and infinitely varied patterns with which they are 

 adorned. Of course, the still more extensive order of the 

 Coleoptera (beetles) present a similar phenomenon in the 

 colours 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 expand 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 or 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 to be formed as 



minute bag-like sacs filled with protoplasm ; the succeeding 



whiteness is caused by the protoplasm being withdrawn and 



the sacs 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 brilliant colours 



seem to be produced from the dull yellow pigment by 



chemical changes which occur within the scales. A few 



days before emergence the scales become fully grown, as 



highly complex structures formed of parallel rows of minute 



cells, each scale with a basal stem which enters a pocket of 



the skin or membrane, which pockets send out roots which 



seem to penetrate through the skin. 1 Another complication 



1 This description is from Mr. A. G. Mayer's paper on the Development 

 of the Wing Scales of Butterflies and Moths (Bull. Mus. Comp. Zool. Harv. 

 Coll., June 1896), so far as I can give it in a very condensed abstract. 



