ei) 
part u.| THE INSECTS WHICH VISIT FLOWERS. 39 
gently between them. A remarkable peculiarity of the flaps, 
shown in Fig. 5, makes them admirably adapted for seizing the 
pollen, for grinding it down, and for passing it backwards; the 
apposed surfaces of the two flaps being closely set with parallel 
: ridges of chitin, by which the pollen-grains are easily held fast, and 
_ shoved into the entrance of the groove (d). 
2 
- 
7 
- 
a 
= 
= 
— 
— 
Fic. 5.—Proboscis of Eristalis tenax, more highly magnified. 
1.—The greater part of the proboscis of Eristalis tenaz, L., with the flaps applied together, and 
the mouth parts slightly separated ; seen from above. When the pieces h and i are depressed in the 
groove d, the mouth parts are in the position for feeding on pollen. 
‘ eon end of the same proboscis with the flaps separated to show the chitinous ridges on their 
nner sides. 
Lettering as in the preceding figure, 
This peculiarity is undoubtedly developed in connection with a 
pollen diet, for it is obviously advantageous thereto; and it is only 
found in those families of Diptera which visit flowers to obtain 
both pollen and honey (Syrphide, Muscide, Stratiomyide), and is 
absent in those which avail themselves of honey only (Bombyliide, 
