PRESERVING AND STUDYING INSECTS 347 



the specimens covered with a cover glass. This method is far 

 from satisfactory, as the balsam soon clouds, but at present it is 

 the only thing that can be recommended as a permanent mount. 



Two methods are employed in mounting scale insects. The 

 entire scales are mounted by taking a thin strip of bark on which 

 is found a colony of scales, and after leaving it in the cyanide 

 bottle for twenty-four hours, it is placed between two pieces of 

 celluloid. The two plates of celluloid are held apart by a cell cut 

 out of cardboard, and the entire mount sealed with passe-partout 

 tape. The thickness of the cell depends upon the thickness of the 

 piece of bark to be mounted. It will be found very convenient to 

 have these cells cut the size of an ordinary microscope slide. This 

 form of mounting will do only for very superficial study, and some 

 of the scales must be cleared and mounted in balsam. This is 

 done by removing the scales from the bark and, in the case of the 

 armored or flat scales, removing the insects from under the scales 

 and placing them in a small test tube with caustic potash solution. 

 These should be boiled until clear, the length of time depending 

 upon the thickness of the scales. They are then washed in water 

 by sedimentation ; that is, the test tube is filled with water and 

 held in a vertical position until the scales have settled to the bot- 

 tom. The water is then nearly all drawn off with a pipette, and the 

 process is repeated. After all of the caustic potash has been re- 

 moved, they are washed in 95 per cent alcohol and cleared in 

 xylol. They should then be removed to a glass slide by means of 

 a camel's-hair brush, and mounted in balsam. Since the last seg- 

 ment of the abdomen, the pygidium, is the only part of the insect 

 used in classification, this is all that it is necessary to mount. 



Neuroptera, Mecoptera, and Tricoptera. These forms are all 

 pinned through the metathorax ; the wings may or may not be 

 spread, but it is usually best to spread the wings at least on one 

 side of the body, the hind borders of the front pair of wings being 

 brought forward at right angles to the body. 



Lepidoptera (Fig. 480). In mounting Lepidoptera the pin is run 

 through the mesothorax or metathorax; the wings are always spread, 

 the front pair being brought forward until the hind margins are at 

 right angles to the body. This rule is invariably followed both 

 with the moths and butterflies. The smaller forms are usually 



