148 EVENINGS AT THE MICROSCOPE. 



cutting-edge. Next, having severed the head, you must 

 place it in a drop of water, between the plates of your 

 compressorium, the graduated pressure of which, by 

 means of the screw, will cause the organs of the mouth 

 to open and expand separately. Finally, you must have 

 a good instrument, and a high power : less than 600 

 diameters will not avail to bring out distinctly the 

 toothing of the mandibles and labrum ; and even then 

 you will need delicate manipulation and a practised eye. 

 But the object is worthy of the care bestowed upon it. 



Once more. Let us submit to examination the com- 

 plex case of instruments wherewith the Gnat performs her 

 unwelcome yet skilful surgery. I say " her," because 

 among the Gnats also, as I have just intimated, it is the 

 females only who possess skill in the art of bleeding ; 

 the males being innocent of any share in it, and being 

 indeed unprovided with the needful implements. 



Here is a large specimen, resting with raised hind legs 

 on the ceiling, and now in alarm off with shrill humming 

 flight to the window. I decapitate her without com- 

 punction, as it is but a fair penalty for her murderous 

 deeds ; and as, of old, the axeman held up " the head 

 of a traitor " to public gaze, so I lay this head on the 

 glass of the compressorium for your contemplation. 



And before I apply pressure to the glass-plate, devote 

 a moment's attention to the head as a whole. First, the 

 head itself is a hemisphere, almost wholly occupied with 

 the two compound eyes, which present the beautiful ap- 

 pearance of a globe of black velvet, studded with gold 

 buttons arranged in lines crossing each other at right 

 angles. The summit of the head, where the two com- 

 pound eyes unite, bears a sort of rounded pedestal, the 

 area of which forms the sole part of the head not covered 

 by the organs of vision. On this are placed, side by side, 

 the two antennae, springing from rounded bulbous bases; 

 they consist of twelve (exclusive of the basal bulb) cylin- 



