38 THE FERTILISATION OF FLOWERS. [PART IT. 
pieces kk arise on each side somewhat below the coalesced man- 
dibles (77), and bear palps on their outer sides; these are there- 
fore, without doubt, to be looked upon as the maxille with their 
palps, while the basal parts of the maxilla have coalesced with 
the base of the lower lip (g) (/abiwm), and are dimly visible below 
the skin (4,/', Fig. 4). The contractile piece (f) and the piece 
supported by the chitinous plate (¢), form together the free 
superiorly-grooved anterior part of the lower lip; f and e 
probably represent the submentum and mentum. The flaps 
(cc) are probably not the palps but the modified paraglossz 
borne on the ligula, though Burmeister prefers to consider them 
as labial palps. 
Let us now consider how these structures are disposed, 
(1) when feeding on pollen ; (2) when sucking honey; (3) when 
at rest. 
(1). In feeding on pollen, the fly stretches out its extensible 
proboscis, moving it, according to need, straight forwards, out- 
wards, or upwards, grasps with the two flaps at its extremity a 
little mass of pollen, rubs this down to single grains by a rapid 
motion of the flaps, and passes it backwards by the same motion 
into the groove on the lower lip; in this groove lies the upper lip, 
which is grooved below, and, within that, the chitinous pieces which 
are presumably formed by coalescence of the mandibles, and are now 
prepared to seize the pollen. As soon as the pollen is sent back- 
wards by the terminal flaps, these chitinous pieces separate slightly 
the parts which immediately surround the mouth-orifice, seize the 
pollen now lying in the groove of the lower lip, and thrust it 
backwards into the mouth. After a few seconds the first portion 
is swallowed, and the same series of actions begins anew. When the 
pollen-grains are united into long strings by elastic threads, as in 
(@nothera, an action of the forelegs, alternating with the movements 
just described, is necessary in order to free the pollen-grains from 
the threads. After the fly has torn away a little mass of pollen 
from the anther, it brings up its forefeet to its mouth while stand- 
ing on its mid and hindlegs; then taking the cord of elastic 
threads between its forefeet, and rubbing them together as if 
washing its hands, it tears the threads asunder, and frees proboscis 
and legs from them. Sometimes, to clean the terminal flaps from 
adhering pollen, it takes its proboscis in its forefeet, and rubs it 
1 In Fristalis tenaw, which attains a length of 15 mm., the outstretched proboscis 
is 7 to 8 mm. long; in Z. arbustorwm, which is 10 mm. long, the proboscis is 4 to 5 
mm. long, 
