44 THE FERTILISATION OF FLOWERS. [PART II. 
forwards. The labrum itself is drawn out into a stiff, fine point, 
Both the labrum and the united mandibles, held between the long, 
narrow end-flaps (paraglosse), may easily be stuck into soft tissues. 
I have often seen species of Bombylius thrust their tongues into 
honeyless flowers (e.g. B. canescens, Mik., into Hypericum perforatum), 
and I imagine that here the boring apparatus was being brought 
into action. 
While, so far as I know, the species of Homtuliys and the 
Conopide restrict themselves to the juices of flowers, very many 
other anthophilous flies are in the habit at times of sucking all 
kinds of other, often uncleanly, fluids. Thus, species of Lristalis 
may be seen feeding eagerly in gutters, Scatophaga and Lucilia 
on dung, Sarcophaga on putrid flesh; even Volucella bombylans, 
which is so abundant on flowers, I noticed in May, 1869, feeding 
on a floating carcase, and returning repeatedly to it when driven 
off. Several flowers seem to have acquired an offensive smell in 
relation to these habits of flies. 
Of the second main division of Diptera, the gnats, the larger 
forms, Tipula, Bibio, etc., are of very second-rate importance in the 
fertilisation of flowers ; they occasionally lick fully exposed honey, 
and so act now and then as carriers of pollen. No flower has 
become specially adapted for them. Tiny species of midges, on 
the other hand, eg. Psychoda phalenoides, which hide in dark 
corners in the daytime and fly actively in the evening, are the 
regular fertilisers of the remarkable flowers of Aristolochia 
Clematitis and Arum maculatwm, which afford dark hiding-places 
for their visitors, and hold them in a temporary prison; others 
play an important part in the fertilisation of Adoxa and 
Chrysosplenium. | 
The group of Thysanoptera (Zhrips) are by their small size 
(hardly 1 mm. long at most, and many times less in breadth) fitted 
far better than even the Anthocoride among the Hemiptera or 
Meligethes among the beetles, for entering all sorts of flowers. 
Probably few flowers, if any, are altogether exempt from their 
visits, and though they have seldom been detected in the con- 
veyance of pollen, yet from their great abundance their value as 
fertilisers must not be overlooked. It must be almost impossible 
to exclude these tiny insects, when we try to isolate a plant 
experimentally by means of nets. The Thysanoptera seek both 
pollen and honey. They seize a single pollen-grain in their 
1 Darwin, whose experiments were always marked by admirable precautions, always 
kept in view ‘the possibility of Thysanoptera entering through his nets. 
