HAIRS 



981 



micrograph of the hair of Poly.t:emi8 lagurus, of the family Polij- 

 desmidcK (order ChUognatha), is given in fig. 6 of the frontispiece. 

 This is one of the finest test objects for medium powers. Other 

 minute forms of this class are most beautiful objects under the 

 binocular microscope on account of the remarkable structure and 

 regular arrangement of their hairs. 



In examining the integument of insects and its appendages 

 parts of the surface may be viewed either by reflected or transmitted 

 light, according to their degree of transparence and the nature of 

 their covering. The beetle and butterfly tribes furnish the greater 

 number of the specimens suitable to be viewed as opaque objects ; 

 and nothing is easier than to mqunt portions of the elytra of the 

 former (usually the most showy parts of their 

 bodies), or of the wings of the latter, in the ^ * 



manner described in Chapter VII. The tribe 

 of Curculionidce, in which the surface is beset 

 with scales having the most varied and lustrous 

 hues, is distinguished among Coleoptera for the 

 brilliancy of the objects it affords, the most 

 remarkable in this respect being the well-known 

 Curculio imperialis^ or ' diamond beetle ' of South 

 America, parts of whose elytra, when properly 

 illuminated and looked at with a low power, 

 show like clusters of jewels flashing against a 

 dark velvet ground. In many of the British 

 Curculionidce, which are smaller and far 

 less brilliant, the scales lie at the bottom of 

 little depressions of the surface ; and if the 

 elytra of the diamond beetle be carefully 

 examined, it will be found that each of the 

 clusters of scales which are arranged upon it 

 in rows seems to rise out of a deep pit which 

 sinks in by its side. The transition from scales 

 to hairs is extremely w r ell seen by comparing 

 the different parts of the surface of the diamond 

 beetle with each other. The beauty and bril- 

 liancy of many objects of this kind are increased 

 by mounting them in cells in Canada balsam, 

 even though they are to be viewed with reflected 



light ; other objects, however, are rendered less attractive by this 

 treatment ; and in order to ascertain whether it is likely to improve 

 or to deteriorate the specimen, it is a good plan first to test some 

 other portion of the body having scales of the same kind by touching 

 it with turpentine, and then to mount the part selected as an object, 

 either in balsam or dry, according as the turpentine increases or 

 diminishes the brilliancy of the scales on the spot to which it was 

 applied. Portions of the wings of Lepidoptera are best mounted as 

 opaque objects without any other preparation than gumming them 

 flat down to the disc of the wooden slide, care being taken to avoid 

 disturbing the arrangement of the scales and to keep the objects, 

 when mounted, as secluded as possible from dust. In selecting such 



FIG. 730. A, hair of 

 Myriojjod] B, hair of 

 Dermestes. 



