ENTIRE INSECTS AS MICROSCOPIC OBJECTS. 653 



observer who should desire 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 labours under the embarras cles 

 ricTiesses; for to enter into such a description of the parts of the 

 structure of Insects most interesting to the Microscopist, 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 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 conformation of their minute parts as seen with the Microscope 

 is adequately illustrated. 



510. A considerable number of the smaller Insects — especially 

 those belonging to the Orders CoJeoptera (Beetles), Neuroptera 

 (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 

 tbeir 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 

 translucence allows them to be viewed as Transparent objects ; and 

 these are either to be mounted in Canada Balsam, or in Deane's 

 Gelatine, Glycerine Jelly, or Farrants'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 lio-ht 

 through it, or the softness and delicacy of their textures render a 

 preservative 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 these ' Media. ' 

 Some of the Aquatic Larva? 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 (§ 522). Among these, there is none pre- 

 ferable to the Larva of the Ephemera marginata (Day-fly), which 

 is distinguished by the possession of a number of beautiful appen- 

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



