THE STRUCTURE OF THE BLOW-FLY 141 



the under side of the head, in which the proboscis can be 

 folded up. Hold the fly between the finger and thumb, and 

 while observing it with the lens, press gently on the sides of 

 the head. The proboscis will then be protruded, owing to 

 distension by air. Note the inflation of the basal parts, the 

 movements of the maxillary palps, and the action of the 

 joints. 



The proboscis consists of a basal part (rostrum), which 

 represents the fore part of the head, and the mouth-parts. At 

 the junction of these two divisions of the proboscis will be 

 seen the maxillary palps, two curved, black, single-jointed 

 rods, covered with hairs, very unlike the long three-or-four- 

 jointed palps of a 

 Nemoceran fly 

 (see p. 131). Be- 

 yond these is the 

 labium, a thick 

 and jointed hol- 

 low tube, ending 

 in an oval palette, 

 which forms the 

 rasping surface, 

 while the tube is 

 used for suction. 



The upper surface ^.^ So.-Female blow-fly, dorsal view. X 3- 



of the labium is 



grooved, ' and upon it lies a stiff, dark-coloured rod (the 

 labrum) shaped like a long and veiy narrow steel pen; the 

 labrum is partly overlapped by the sides of the labium. In 

 Dipterous flies with piercing mouth-parts the labrum can be 

 raised by the insect at pleasure, when the piercing imple- 

 ments within are exposed; but in the blow-fly the labrum 

 is never raised, and there is only a single needle within 

 it, which is quite harmless. The palette at the tip of 

 the labium consists of two lobes, sometimes called the 

 labellse. 



Extend the proboscis by pressure on the sides of the head, 

 and then cut it off with a pair of fine scissors, as near the base 

 as possible. Mount it in glycerine, and examine with a low 

 power of the microscope. A permanent preparation may be 

 made by treating the proboscis with caustic potash solution. 



