554 INSECTS AND ARACHNIDA. 



observer who should desh-e thoroughly to work it out, not only 

 for months but for years. Hence in treating of this department 

 in such a work as the present, the author labors under the 

 embarras des riohesses ; for to enter into such a description of the 

 parts of the structure of Insects most interesting to the Micro- 

 scopist, as should 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 tlie hinds 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 speci- 

 mens of each class may be most readily obtained. And thus 

 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 conformation of their minute parts as seen with the Micro- 

 scope is adequately illustrated. 



377. A considerable number of the smaller Insects, — espe- 

 cially those belonging to the orders Coleoptera (beetles), Neurop- 

 tera (dragon fly. May fly, &c.), Hymenoptera (bee, wasp, &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. Full 

 directions on this point, applicable to small and large Insects 

 alike, will be found in all text-books of Entomology. There are 

 some, however, whose translucency allows them to be viewed as 

 transparent objects ; and these are either to be mounted in 

 Canada balsam, or in weak spirit or glycerine, according to the 

 degree in which the horny opacity of their integument requires 

 the assistance of the former to facilitate the transmission of 

 light through it, or the softness and delicacy of their textures 

 renders a preservative liquid more desirable. Thus an ordinary 

 Flea or Bug will best be mounted in the former medium ; 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 the latter. Some of the aquatic larvte of the Diptera and 

 Neuroptera, which are so transparent that their whole internal 

 organization 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 (§ 389). 

 Among these, there is none preferable to the larva of the 

 Ephemera marginata (day fly), which is distinguished by the pos- 

 session of a number of beautiful appendages on its body and 



