152 Sir E. Home on the feet of animals 
It is evident, that when the external edge of this apparatus 
is closely applied to any surface, and the cartilaginous plates 
are raised up, the interstices must become so many vacua, 
and the serrated edge Of each plate will keep a sufficient hold 
of the substance on which it rests, to retain it in that position, 
assisted by the pressure of the surrounding water, without a 
continuance of muscular exertion. 
It thus appears, that the adhesion of the Echineis Remora 
is produced by so many vacua being formed by an apparatus 
worked by the voluntary muscles of the animal, and the pres- 
sure of the surrounding water. 
From the similarity of the mechanism of the under surface 
of the toes of the Lacerta Gecko, there can be no doubt, that 
the purpose to which it is applied, is the same ; but as in the 
one case, the adhesion is to take place under water, and is to 
continue for longer periods, the means are more simple. In 
the other, where the mechanism is to be employed in air, under 
greater disadvantages with respect to gravity, and is to last 
for very short periods, and then immediately afterwards be 
renewed, a more delicate structure of parts, a greater pro- 
portional depth of cavities, and a more complex muscular 
structure becomes necessary. 
Having ascertained the principle on which an animal of so 
large a size as the Lacerta Gecko, is enabled to support itself 
in its progressive motion against gravity, I felt myself more 
competent to enquire into the mechanism by which the com- 
mon fly is enabled, with so much facility, to support itself in 
still more disadvantageous situations. 
In the natural size the feet of the fly are so small, that 
nothing can be determined respecting them ; and when highly 
