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hairs ; further off we find others which differ from the former in being 

 forked like the letter Y. These forks shortly begin to swell at their 

 juncture with each other, and at the margin of the wing the fork is 

 quite tilled up, and the hair has become converted into a large scale. 



These scales exist more or less over the greater part of the body of the 

 insect, the presence of hair being the exception. In some moths and 

 butterflies no hair whatever is to be found — scales alone are seen. 



The scales of insects form, therefore, a connecting link between the 

 hairs and scales of higher animals. 



It is interesting to examine into the anatomical difference between the 

 different hail's and scales we have mentioned as growing on the wing of 

 the " Ithamtea." The single hair consists of an outer or fibrous coating 

 and an inner substance or medulla analogous to, though not identical 

 with, the stnictures found in mammalia. 



Both these increase, but not in an equal ratio. The inner, growing 

 much more rapidly than the outer, divides the latter into dots or ridges, 

 which are connected together by delicate lines in some instances, and 

 by a continuous membrane in others. These dots and ridges, however, 

 are very regular in each class, so that in many cases a butterfly can be 

 identified by the dust off his wing — which proves that there is some 

 other agent at work beyond simple distension. 



To see the inner structiu-e properly the scales must be well rubbed 

 between two plates of glass, to remove the lines. It is then found to be 

 clear, transparent, and usually colourless, but in some cases it is bluish 

 or rose-tinted ; it is of great tenacity, and is capable of much resistance — 

 when torn, it appears to consist of two membranes closely adherent. 



There is reason to believe that the inner structure is nothing more 

 than a duplication of the dermis or inner skin. The lines upon the 

 scales are usually longitudinal ; a few secondary ones may occasionally 

 be seen passing obliquely from the point of insertion of the scale, 

 which are probably due to a puckering of the inner membrane. 



When the lines are close together they form good microscopic tests — 

 they also produce a beautiful play of colours by reflected or transmitted 

 light. The brilliant colours on the wings of many butterflies have no 

 absolute existence, as may be readily demonstrated by the microscope ; 

 they are produced by the light being decomposed when passing through 

 or reflected from fine lines, and in this resemble thin sections of the 

 Haliotis splendens and Mother-of-Pearl. 



Having seen in the insect world how gi-eat is the variety of forms to 

 be met with, and having traced the connection between the most opposite 

 ones and their relation in outward shape at least to corresponding forms 



