154 'SYr E. Home on the feet of animals 
but concave surfaces, as Keller represents them ; a copy of 
which representation is annexed. 
Although the author states them to be concave surfaces, he 
says that they are only used when the fly moves horizontally ; 
but when it moves perpendicularly, or upon the ceiling, they 
are turned up out of the way ; and the progressive motion is 
carried on by fixing the crotchets into the irregularities of 
the surface on which the fly treads, whether glass, porcelain, 
or any other substance. It will, however, scarcely be doubted, 
from the preceding facts, that these concave surfaces are em- 
ployed to form vacua, which enable the fly to move under 
such disadvantageous circumstances upon the same principle 
as the Lacerta Gecko. 
EXPLANATION OF PLATES. 
Plate VII. 
The external form of the Lacerta Gecko. 
Plate VIII. 
Fig. 1. The under surface of one of the toes of the Lacerta 
Gecko of the natural size. 
Fig. 2. A toe dissected to show the appearance of the 
pockets on its under surface, their serrated cuticular edge, 
the depth of the pockets, and the small muscles by which they 
are drawn open, the parts much magnified. 
aa The two muscles which lie on the sides of the bones of 
the toe, with their tendons inserted into the last bone close to 
the root of the claw. From these tendons the muscles belong- 
ing to the pocket go off. 
Fig. 3. The upper surface of the head of the Echineis 
Remora, to show the apparatus by which the animal has a 
