ANATOMY AND PHYSIOLOGY. 105 
but rounded off, so as to leave room for the free play 
of the foot, which forms a kind of sixth tarsal jomt in 
which the limb ends. 
The most prominent feature in the foot is a large 
pair of claws, one on each side. These, it should be 
particularly noticed, are simple in the Vespide, while 
in the Eumenide they are toothed in their concavity. 
This rule has no exceptions.* Between the tarsal 
hooks we find the pulvilli or cushions on which the 
insect treads. These are covered on their plantar 
surface with minute hairs, some of which are hooked 
at their extremities, and others are bulbous, remind- 
ing one of the bulbous suckers with which the arms 
of the star-fish are provided. It is by means of 
these bulbs that the foot clings to smooth and 
polished surfaces; but whether by atmospheric 
pressure only, or by the aid of a glutinous secre- 
tion, does not seem absolutely certain.tf Though 
the increased difficulty with which a fly makes its 
Way over a pane of glass damped by the breath 
seems strongly to favour the first opinion. 
The insect sucker consists essentially of a hair, 
with its extremity dilated into a bulb and hollowed 
out in the centre. This is seen in the most perfectly 
developed form on the fore-legs of our great water- 
beetle, Dyticus marginalis ; and the same form of 
instrument, only very much reduced in size, is set 
over the pulvilli of the fly’s foot, where there is no 
great difficulty in recognizing it. It requires, how- 
ever, a high power of the microscope, and a careful 
* De Saussure, ‘ Guépes Solitaires,’ tome I, p. xix. 
- + See on all this subject, Tuffen West, On the Foot of the Fly, 
‘ Linnean Transactions,’ Vol. XXIII, p. 393. 
