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 complex 

 case of instruments wherewith the Gnat performs her un- 

 welcome 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 unpro- 

 vided 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 antennas, springing from rounded bulbous bases ; 

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



