40 THE FERTILISATION OF FLOWERS. [PART II. 
Empide, and Conopide), and in the gnats, which are also purely 
suctorial.} 
(2). In sucking honey the Syrphide place the grooved upper lip 
(h, 1, Fig. 5), and the chitinous piece (7) together, to form a tube 
which is inclined downwards and inclosed within the groove on 
the lower lip. The terminal flaps may now be useful in two ways; 
they may either be laid close together (as in 1, Fig. 5) while the 
membranous middle joint (7) of the lower lip is so far drawn in that 
the suctorial apparatus inclosed within the groove of the lower lip 
protrudes in front of the flaps and dips into the fluid to be sucked ; 
or they spread out the flaps wide apart so that their rough inner 
surfaces rest upon the support, and the point of the suctorial 
apparatus protrudes at the end of the groove on the lower lip. 
Flies with swollen cushion-shaped flaps (Syrphus balteatus, Fig. 7) 
act usually in the latter way, those with long narrow flaps (Rhingia, 
Fig. 6) adopt exclusively the former. Both pollen-grains and fluid 
which have been carried into the tube formed by the chitinous 
pieces h and 1, are aided in their passage to the mouth by means of 
the sucking stomach in connection with it. The maxille and their 
palps seem to play no part either in sucking or in feeding on 
pollen, and hence must be looked upon as useless appendages in 
the Syrphide. 
(3). To guard the proboscis when at rest, the fly draws the 
membranous basal piece g backwards and downwards, the upper lip, 
mandible, and maxillz, with their palps fold upwards, the contrac- 
tile middle piece (/’) is closely drawn up, forming a few membranous 
folds at the lowest part of the proboscis, the horny plate (e) and the 
flaps (c) fold upwards and forwards, and the whole proboscis now lies 
so deeply hidden in the deep cavity underneath the snout-like 
prolongation of the head (m, 1, 2, Fig. 4), that at most the terminal 
flaps protrude slightly (1, Fig. 4). On examining the head now 
from below (2, Fig. 4) one sees in the cavity only the flaps ¢ ¢’, 
and beneath them the upper part of the chitinous plate (e), whose 
lower part lies hidden in the folds of the contractile part of the 
proboscis. 
A further advance on these adaptations, fitting them still more 
completely for their threefold requirements, is conceivable, if to 
a still more elongated proboscis there is added a greater develop- 
ment of the snout-like prolongation of the head which covers it 
1 | have never observed the Tabanide to feed on pollen, though their end-flaps are 
roughened with chitinous ridges; but I have often found Tabanus micans and 7, 
lwridus on flowers, and I think it not unlikely that they sometimes feed on pollen, 
