THE LEGS. 
31 
in both, the femora and tibiae of Aphides, and may be 
easily seen after treatment with acetic acid. They 
often also become obvious after the insect has been 
some time mounted in Canada balsam. In the femur 
the muscles are compounded of broad fasciculi. 
The base of the tibia is expanded into a soft cushion 
or retractile sac, which is regulated by a distinct 
muscle and ligament. Probably this organ acts as a 
pulvillus, to secure foothold on the glossy surfaces of 
leaves. 
The tarsus is attached to the horny plate of the tibia 
by a fine joint, and an elastic membrane. 
I 
