part u.] THE INSECTS WHICH VISIT FLOWERS. 37 
take the most specialised and most abundant of the Syrphide, 
Eristalis and Rhingia. | 
In £ristalis the outstretched proboscis is seen to be composed of 
three segments (Fig. 4, 4, 5, 6, and Fig. 5, 1): (1) the mem- 
branous basal piece (9), which bears anteriorly two unpaired (A, 7) 
and two paired (& &) elongated chitinous pieces, and external to the 
latter two palps (J 7); (2) the membranous and very contractile 
middle segment (7), only clearly separated on the lower surface ; 
and (8) the extremity of the proboscis, supported beneath by a 
stiff chitinous plate (c), and bearing at its apex two contiguous 
ee st 
Fic. 4.—Mouth-parts of Eristalis (7: 1). 
: 1.—Head of E. arbustorum with retracted proboscis, from the side. 
pe 2.—Ditto, from below. 
* $,—Ditto, with extended proboscis, from above. 
g y 4.—Extended proboscis of E. tenaw, from the side. 
_~*- 5,—Ditto, from below. 
_,  6.—Ditto, from above. 
, a, eye; bb, antenney; ec, end-flaps of proboscis; ¢/c’, their inferior segment ; d, ve on the 
_~ upper side of the point of the proboscis ; e, harder chitinous piece on the under side of the point of 
the proboscis; jf, contractile middle part of the proboscis; g, contractile base of proboscis; h, 
upper lip (labrum), grooved underneath to receive the unpaired piece (i), which probably represents 
the two fused mandibles; k, maxilla; 1, maxillary palp ; mm, edges of the cavity on the under side 
of the head into which the whole proboscis is withdrawn ; n, occipital foramen. 
flaps or lips each of two parts (cc and ¢'c’), and on its upper 
surface a longitudinal groove. Of the chitinous pieces at the 
end of the first segment of the proboscis, only the superior un- 
paired one (h), which is prolonged under the membrane to the head, 
can be looked upon as an upper lip (/abrum); the lower one (7) seems 
to be formed by coalescence of the two mandibles. The upper lip 
(h) forms, with its concave side, a groove directed downwards into 
which the piece 7 can be completely withdrawn ; between the bases 
_ of these pieces 2 and 7, when drawn wide apart, the small opening 
_ of the mouth can be seen. The free ends of the two chitinous 
ery ee eo 
