OF MICROSCOPIC OBJECTS. 69 



the cover down it may be left to dry, or you may hold the slide 

 over a spirit-lamp for a few seconds before pressing down the 

 cover. If heat is not applied, they are much longer in drying but 

 are more transparent. If made too hot the boiling disarranges 

 the objects, and if carried too far will leave only the resin of the 

 balsam, rendering it so brittle that the cover is apt to fly off by a 

 fall or any jar producing sufficient percussion. Never lift the cover 

 up if possible, during the operation, as there is danger of admitting 

 air. A few bubbles may appear immediately after mounting, but 

 generally subside after a few hours, being only the chloroform or 

 turpentine in a state of vapour, which becomes condensed." 



This method of preparing and mounting insects I can strongly 

 recommend as giving first-rate results ; but where the specimens 

 are small they seldom need the soaking in caustic potash which 

 larger ones must have. It is only necessary to leave them awhile 

 in turpentine, especially when they have been first dried with gen- 

 tle pressure between two glasses, and then mount with balsam in 

 the ordinary way. 



Amongst the insect tribes there is abundant employment, espe- 

 cially for the lower powers of the microscope. But if the deep- 

 er wonders and beauties of the animal economy are to be sought 

 out and studied, it is desirable that the various parts should be set 

 separately, in order that they may receive a more undivided at- 

 tention, as well as to render them capable of being dealt with un- 

 der the higher powers. We will, therefore, briefly consider the 

 treatment which the different portions require. 



The eyes of the butterflies, and indeed of almost all insects, 

 afford materials for a study which is complete in itself. When 

 examined with a tolerably high power, instead of finding each eye 

 with an unbroken spherical surface, it is seen that many are com- 

 posed of thousands of hexagonal divisions, each being the outer 

 surface of a separate portion termed the ocellus. In others these 

 divisions are square ; but in all there is a layer of dark pigment 

 surrounding their lower parts. The ocelli may be partly removed 

 from the eye, which will show how their tapering forms are ar- 

 ranged. But here we have to consider how to place them in bal- 

 sam for preservation. The eve being removed from the insect, 

 and the dark pigment removed by the use of a cainel-hair pencil, 



