THE MICROSCOPICAL PREPARATION OF INSECTS 221 



water under the microscope. I have specimens of various 

 species of Hsematopinus, where the result of striking the 

 happy medium is that not only the exo-skeleton but also 

 the tracheal system is beautifully displayed. 



Some delicate insects would require the solution to 

 be not stronger than 2 per cent, or the boiling might be 

 limited to five minutes or even less. Others, especially 

 such as have delicate wings, should not be boiled at all, 

 but left to steep in cold KOH solution until their internal 

 tissues have been sufficiently acted upon. This will take 

 from one to several days. 



Sometimes a heavy-bodied insect has comparatively 

 delicate wings, which would be apt to be damaged if 

 subjected to the amount of boiling required for the body. 

 In very special cases I have occasionally found it advantage- 

 ous to remove the wings carefully before the treatment 

 with KOH, and only replace them when the insect 

 is laid out in balsam on the slide. Lest they should float 

 from their places when the cover-glass is put on, this should 

 not be done till next day, the preparation meantime being 

 protected from dust. A fresh drop of balsam is then to 

 be placed on the specimen, and a warmed cover-glass 

 applied. 



In the case of Hippobosca equina, for example, one 

 may thus boil the coarse body safely for twenty minutes 

 in 10 per cent. KOH, which would have been ruinous to 

 the fragile wings. 



Fly Maggots are specially troublesome to clear in 

 KOH, the reason being, I suppose, that the integument 

 is not pierced by the laterally placed spiracles usual in 

 other forms. To remedy this, one has to puncture the 

 maggot by pricking with a needle in one or two places 

 towards the middle of the body. 



Many insects become too transparent by the KOH 

 treatment, and yet important details of their structure 

 cannot be shown up in preparations not rendered trans- 

 parent. In this dilemma one has recourse to stains. I 

 have found for this purpose, i.e., for staining the chitinous 

 exo-skeleton, acid fuchsin entirely satisfactory. It is most 



