THE MICROSCOPICAL PREPARATION OF INSECTS 227 



object was to display the mouth parts, and which were 

 prepared as follows : 



Boil for three minutes in 10 per cent. KOH to open and 



separate the mouth parts. 

 Wash in distilled water. 



Treat with glacial acetic acid twelve to twenty-four hours. 

 Wash. 

 Mount in Farrant's solution (preferably) because of its low 



refractive index, and because in this medium it is easier to 



lay out the slender and delicate appendages upon which 



glycerine jelly is apt to set too heavily. 



For sealing up I use balsam, because if the cover-glass 

 gets broken at any time it is easier to renew it and save 

 the preparation, than is the case where a black cement has 

 been used. 



To Dr Ashworth I owe the following directions for 

 mounting in formalin, a useful method when it is desired to 

 preserve small creatures as far as possible in their natural 

 aspect : 



Fill an excavated glass slide with 10 per cent, formalin, put in 

 the insect, cover, and seal up with balsam. The insect 

 might be previously sometvhat flattened out in formalin to 

 put its appendages in position, but not pressed so as to 

 squeeze it. The water used to dilute the formalin must be 

 well boiled, or bubbles will appear in the preparation. 



Dr Ashworth advises that the insect be killed by boiling 

 water, and transferred .to alcohol 70 to 85 per cent. Before 

 mounting get down to water and then into a relatively large 

 quantity of 10 per cent, formalin. 



I found this good, for instance with ant larvae, when 

 I wished to display the curious forked hairs, which in balsam 

 or glycerine become too transparent. 



For dissections of insects I have no suggestions to add to 

 the usual routine of fixing, staining, and mounting on the 

 slide, unless it be to substitute sometimes Unna's polychrome 

 methylene blue for the usual borax or alum carmine. It is 

 differentiated with alcohol, and, to my thinking, the blue 

 colour is pleasanter to the eye than red. 



