MOUNTING- INSECTS 973 



be at all comparable in fulness with the accounts which it has been 

 thought desirable to give of other classes would swell out the 

 volume to an inconvenient bulk ; and no course seems open but to 

 limit the treatment of the subject to a notice of the kinds of 

 objects which are likely to prove most generally interesting, with a 

 few illustrations that may serve to make the descriptions more clear, 

 and with an enumeration of some of the sources whence a variety 

 of specimens of each class may be most readily obtained. And this 

 limitation is the less to be regretted, since there already exist in 

 our language numerous elementary treatises on entomology, wherein 

 the general structure of insects is fully explained, and the conforma- 

 tion of their minute parts as seen with the microscope is adequately 

 illustrated. 1 



A considerable number of the smaller insects especially those 

 belonging to the orders Coleoptera (beetles), ffieuroptera (dragon-fly, 

 May-fly, &c.), Hymenoptera (bee, w r asp, &c.), and Diptera (two-winged 

 flies) may be mounted entire as opaque objects for low magnifying 

 powers, care being taken to spread out their legs, wings, &c., so as 

 adequately to display them, which may be accomplished, even after 

 they have dried in other positions, by softening them by steeping 

 them in hot water, or, where this is objectionable, by exposing 

 them to steam. Directions on this point, applicable to small and 

 large insects alike, may be found in various text -books of ento- 

 mology. There are some, however, whose translucence allows them 

 to be viewed as transparent objects, and these are either to 

 be mounted in Canada balsam or in Dean's medium, glycerin 

 jelly, or Farrant's gum, according to the degree in which the horny 

 opacity of their integument requires the assistance of the balsam to 

 facilitate the transmission of light through it, or the softness and 

 delicacy of their textures render an aqueous medium more desirable. 

 Thus an ordinary flea or bug will best be mounted in balsam ; but 

 the various parasites of the louse kind, with some or other of which 

 almost every kind of animal is affected, should be set up in some of 

 the 'media.' Some of the aquatic Iarva3 of the Diptera and Neuro- 

 ptera, which are so transparent that their whole internal organisa- 

 tion can be made out without dissection, are very beautiful and 

 interesting objects when examined in the living state, especially 

 because they allow the circulation of the blood and the action of the 

 dorsal vessel to be discerned. Among these there is none prefer- 

 able to the larva of the Ephemera marginata (day-fly), which is dis- 

 tinguished by the possession of a number of beautiful appendages 

 on its body and tail, and is, moreover, an extremely common 

 inhabitant of our ponds and streams. This insect passes two or 

 even three years in its larval state, and during this time it 

 repeatedly throws off its skin ; the cast skin, when perfect, is an 

 object of extreme beauty, since, as it formed a complete sheath to 

 the various appendages of the body and tail, it continues to exhibit 

 their outlines with the utmost delicacy ; and by keeping these larvae 



1 An excellent introduction to the study of insects will be found in The Structure 

 and Life-history of the Cockroach, by L. C. Miall and A. Denny (London, 1886). 

 See also Dr. D. Sharp in the Cambridge Natural History. 



