DIPTERA—HOVER-FLIES 



175 



elongated chitinous pieces, with two palps (/, I) external to the latter. (2) The 

 equally membranous and very contractile middle segment {/), which, however, is 

 clearly demarcated on the lower side only. (3) The tip of the proboscis, which 

 is supported beneath by a stiflf chitinous plate {c), and bears at its apex two con- 

 tiguous bifid flaps or lips {c c and c' (/), while its upper surface is traversed by 

 a longitudinal groove {d). Of the chitinous pieces at the end of the basal segment 

 of the proboscis, the upper unpaired one {h), which is prolonged under the skin to 

 the head (Fig. 72, 4, 6, h), can be regarded as an upper lip (labrum) : while the lower 



Fig. 73. Proboscis of Eristalis ienax^ highly magnified (after Hermann Muller). (i) Most of the 

 proboscis of Eristalis tenax Z.., with the flaps applied together and the mouth-parts slightly separated ; 

 seen from the right and above. When the pieces h and i are pressed down into the groove t/, the mouth- 

 parts are in the position for feeding on pollen. (2) The end of the same proboscis with the end-flaps 

 pressed apart to show the chitinous ridges on their inner sides. References as in Fig. 72. 



unpaired one {i) seems to have been formed by fusion of the two mandibles. The 

 concave side of the upper lip (A) serves as a downwardly directed groove, into which 

 the piece / can be completely withdrawn. The small mouth-opening can be seen 

 between the bases of these pieces h and i, when they are drawn widely apart. The 

 free ends of the two sharp chitinous pieces {k k) arise on either side somewhat below 

 the fused mandibles (z), and bear palps on their outer sides. These are therefore 

 undoubtedly to be looked upon as the laciniae with their maxillary palps, while the 

 bases of the maxillae have fused with the bases of the lower lip {g) (labium), and are 



