whose progressive motion is against gravity. 155 
power of adhering to the surface on which it is placed, of the 
natural size. One half of this apparatus has the cartilaginous 
plates closed, the other open. 
Fig. 4. The under surface of the foot of the house-fly 
highly magnified, showing the two concavities by which the 
foot attaches itself to the surface on which it is placed, and two 
claws for laying hold. Copied from a plate by G. Adams, 
published in 1 746. 
Fig. 5. Another view of the same parts copied from a plate 
published in 1766, taken from a drawing of Christofle 
Keller, painter at Nuremberg. 
