72 PREPARATION AND MOUNTING 



which is effected by tracheae or hollow tubes, which generally run 

 through the body in one or more large trunks, branching out on 

 every side. These terminate at the surface in openings, which 

 are termed spiracles, or breathing organs. The tracheae often pre- 

 sent the appearance of tubes constructed by a twisted thread, 

 somewhat resembling the spiral fibres of some plants. These are 

 very beautiful objects, and are generally mounted in balsam, for 

 which reason they are mentioned here ; but as they evidently be- 

 long to the " dissecting portion," they will be fully treated of in 

 another place. 



Amongst the parasitic insects a great variety of microscopic 

 subjects will be found. As these are usually small, they may be 

 killed by immersion in spirits of turpentine ; and if at all opaque, 

 may be allowed to remain in the liquid until transparent enough, 

 and then mounted in Canada balsam. 



The acarida, or mites and ticks, are well known ; none, perhaps, 

 better than those which are so often found upon cheese. Flour, 

 sugars, figs, and other eatables, are much infested by them ; 

 whilst the diseases called the itch in man, and the mange in animals, 

 are produced by creatures belonging to this tribe. These animals 

 are sometimes mounted by simply steeping them in turpentine, 

 and proceeding as with other insects. The " Micrographic Dic- 

 tionary" gives the following directions as to mounting parts of 

 these : " The parts of the mouth and the legs, upon which the cha- 

 racters are usually founded, may be best made out by crushing the 

 animals upon a slide with a thin glass cover, and washing away 

 the exuding substance with water ; sometimes hot solution of 

 potash is requisite, with the subsequent addition of acetic acid and 

 further washing. When afterwards dried and immersed in Canada 

 balsam, the various parts become beautifully distinct, and may be 

 permanently preserved." 



Feathers of different kinds of birds are usually mounted in bal- 

 sam when required to show much of the structure. This is par- 

 ticularly interesting when the feathers are small, as they then 

 show the inner substance, or pith, as it may be termed, with the 

 cells, &c. The " pinnae," or soft branches of the feathers, will be 

 found of various constructions ; some possessing hooks along one 

 side, whereby they fasten themselves to their neighbours ; others 



