DIPTERA—HOVER-FLIES  . 177 
to be enclosed in the labial groove. The insect now uses the end-flaps in one of two 
ways: it either folds them together (as in Fig. 73, 1) while the membranous middle 
piece (/) of the labium is so far retracted that the suctorial apparatus enclosed in the 
labial groove protrudes in front of the flaps and dips into the fluid to be sucked ; 
or else it spreads out and flattens the flaps so that their rough inner surfaces are 
closely applied to the flower, and the tip of the suctorial apparatus protrudes from 
the end of the labial groove. Flies with swollen, cushioned-shaped flaps (Syrphus 
balteatus, Fig. 75) usually behave in the latter way, those with long, narrow flaps 
(Rhingia, Fig. 74) invariably adopt the former. Both pollen-grains and fluid which 
have been carried into the tube formed by the chitinous pieces 4 and 2, are aided in 
their passage to the mouth by dilatation of the sucking stomach. The laciniae and 
maxillary palps seem to play no part either in sucking or in feeding on pollen, and 
hence must be looked upon as useless appendages. 
3. In order to bring the proboscis into the sheltered rest posttion the fly draws 
the musculo-membranous basal piece (g) backwards and downwards, the labrum, 
mandibular piece, maxillae, and maxillary palps fold together above, and the very 
contractile middle piece (/) is com- 
pletely retracted, being thrown into a 
few membranous folds at the lowest 
part of the proboscis. The chitinous 
plate (e) and the end-flaps (c) simul- 
taneously fold upwards and forwards, 
and the complicated proboscis (equally 
adapted for pollen-eating and nectar- 
sucking) now _lies,so deeply hidden Fic. 74. Proboscis of Rhingia rostrata (after Herm. 
in the deep cavity underneath the Miller). (1) Head with completely retracted proboscis ; seen 
. * from the side. (2) The same, at the moment the proboscis 
snout-like prolongation of the head begins to unfold. (3) The same, with proboscis completely 
(Fig. 92, Ly 2; m), that at most the end- extended. (4) Head with completely retracted proboscis; 
F . seen from below; (enlarged twice as much as (1), (2), and (3).) 
flaps protrude a little (Fig. 72,1). If References as in Fig. 72. 
the head is now examined from below 
(Fig. 72, 2), nothing will be seen in the cavity but the end-flaps (¢c’), and beneath 
these the upper part of the chitinous plate (e), of which the lower part lies in the 
folds of skin belonging to the contractile part of the proboscis. 
An advance on these adaptations, furthering convenience in eating pollen, 
enabling more deeply seated nectar to be sucked, and rendering complete shelter 
of the proboscis under the head possible, would result from the greater elongation 
of this organ, with concomitant development of the snout-like prolongation of the 
head. Such a state of things finds its fullest expression in Rhingia (Fig. 74), where 
the proboscis (11-12 mm. long) exceeds the whole body (10 mm.) in length, being 
unsurpassed in this respect by any indigenous fly *. 
This hover-fly takes a foremost place among our native Diptera, not only in 
regard to the length of its proboscis, but also with reference to its power of detecting 
deeply hidden nectar. There is scarcely a single flower with nectar it can reach 
1 Bombylius discolor Mk. alone equals it in length of proboscis: Bombylius major Z. 
approaches it (Io mm.). 
DAVIS N 
