TO POLISHED VERTICAL SURFACES. 221 
hypothesis may be ascertained, I am solicitous to 
direct the attention of naturalists. 
I am aware that the males of several aquatic beetles 
have the tarsi of the first and second pairs of legs 
supplied on the underside with numerous cup-shaped 
suckers of various sizes, which have their edges (the 
larger ones at least) beautifully fringed with delicate 
hairs. These suckers, which probably serve to faci- 
litate the intercourse of the sexes, are remarkably 
conspicuous on the tarsi of the males of a very com- 
mon species, Dyticus marginalis, and unquestionably 
give them a firm hold of smooth objects occurring in 
water, a liquid whose specific gravity rather exceeds 
their own ; but that they are inadequate to the sup- 
port of this insect, the average weight of which is 
about twenty-eight grains, on the vertical sides of dry 
polished bodies, in so rare a medium as air, [ have 
had frequent opportunities of remarking. My chief 
object in adverting to these singular organs, on the 
present occasion, is to guard entomologists against 
the error of supposing that they correspond to the 
pulvilli of insects, which, as I have attempted to 
show, differ from them essentially both in structure 
and function. 
Having demonstrated the insufficiency of the re- 
ceived explanation of the movements of flies on 
polished perpendicular surfaces, I shall now endeavour 
to establish a more satisfactory one in its place. 
In pursuing my experiments with the House-fly I 
