50 



BULLETIN 67, UNITED STATES NATIONAL MUSEUM. 



especially if of high power, is apt to injure the eyesight. A half- 

 inch lens will be found as useful as any for most insect work. 

 For Lepidoptera a three-fourths or an inch lens will be useful. For 

 the minute insects a one-fourth inch lens is used by many, but a 

 compound microscope is better for the eyes. 



An ordinary lens may sometimes be used to advantage in the field 

 by fitting a piece of cork in the handle, and sticking an insect pin 



obliquely through it so that the point of 

 the pin is at the focal distance of the lens. 

 A strong reading glass is very useful in 

 looking over boxes of specimens. 



Dissecting microscopes sold by most 

 dealers are of great value and should be 

 more generally used. The compound 

 microscope is necessary to all who en- 

 deavor to do some original work with 

 small insects, or to study the anatomy of 

 insects. There are various firms, a list of 

 which is given in the back of this article, 

 that supply these, as well as all accesso- 

 ries, slides, cover glasses, stains, etc. In 

 these matters one must consult his means, 

 but a useful instrument can be obtained 

 for about $50. For studying the exterior 

 structure of insects, it is not necessary to 

 have much apparatus known as the sub- 

 stage, nor more than one or two eyepieces 

 and objectives. Many microscopes are so 

 fitted that one can revolve the mirror 

 above the stage and reflect light from 

 above upon the insect. For examining 

 an insect it is well to fasten a cork to a 

 glass slide and stick the pin in this cork. 

 The cork may be fastened to the slide 

 as follows: Drop a little Canada balsam 

 on the slide, heat 

 from beneath, and then put the cork in it. 

 will be held firmly to the slide. 



KILLING INSECTS. 



Fig. 92.— A cyanide bottle with 



PAPER STRIPS TO GIVE SUPPORT TO 

 THE INSECTS. 



it to almost boiling 

 When cold, the cork 



A bottle or jar (fig. 92) containing a poison is used by all ento- 

 mologists to kill their captures. The poison ordinarily used is potas- 

 sium cyanide, a hard, white substance, which can be purchased at 

 drug stores. There are various ways of preparing a bottle or vial. 

 The usual way is to place the cyanide, broken up into a few lumps, 



