49 THE FERTILISATION OF FLOWERS. [parr us. 
of flowers. Of these forms the first two families both suck honey 
and feed on pollen; the last three suck honey only. 
The pollen-eating Muscide and Stra- 
tiomyide have the same soft, cushion- 
shaped, swollen end-flaps, and the same 
chitinous ridges thereon, as the Syrphide ; 
and in spite of some structural differences, 
they use their mouth-organs in the same 
way, and retract them when at rest into 
a cavity below the head. The merely suc- 
torial species of Bombylius, Empis, and 
Conops have end-flaps not provided with 
soft cushions with horny ridges, but 
formed simply of strong chitinous plates, 
which serve to transmit the suctorial 
apparatus; and the proboscis cannot be 
withdrawn into a cavity. So we may con- 
‘i, 
f— 
any. Dosbuatis of a clude that the power of withdrawing the 
balteatus, De G. ia 7 7 : 
eee ey proboscis into a cavity below the head is 
Lettering as in Fig. 2. of advantage only as a protection for the 
pollen-feeding apparatus, and has been 
developed indirectly in relation to anthophilous habits, like the 
snout-like or beak-like prolongation of the head in Syrphide. 
Of the purely suctorial flies, the species of Hmpis carry their 
thin, straight proboscis directed downwards, and use it preferably 
in that position; accordingly they resort chiefly to erect flowers, 
into which they can plunge their proboscis vertically. If the 
flower is tubular, and so long as to require it, they thrust the | 
whole head down into the tube, an action which the small size 
of the head facilitates. The chitinous piece formed by coalescence 
of the mandibles is produced into a sharp, lancet-shaped plate 
(I used Hmpis tesselatum for investigation), which, guided by the 
elliptical end-flaps, is used for boring into juicy structures, such as 
the inner wall of the spur in Orchis. Any considerable increase 
in length in a downward-directed proboscis is clearly impossible 
without the development of a joint. 
In the habits of the Hmpide we see clearly the transition from 
blood-sucking to honey-sucking. Sometimes in a single species 
the females, which require more nourishment, are blood-suckers, 
while the males suck honey only.! In Paltostoma torrentium 
(Blepharoceride) two different kinds of females exist together, one 
' H. Miiller, Natwre, vol, xxiv. p. 214 ; Kosmos, vol. ix. pp. 415-417. 
