No. 499] THE LEG TENDONS OF INSECTS 455 



molt so that the tubular character can never he made 

 out. In the case of the extensor tendon of the knee the 

 enlarged disk must require a considerable stretching of 

 the portion of the tendon further out to enable it to pass. 



The tendon of the claw is very short up to the last 

 molt in the case of plant lice. The structure at the 

 end of the last tarsal joint is shown in Fig. 2. At 

 the extreme end of the foot there are two processes 

 over which the base of the claws rotate. The only 

 other attachment aside from the soft articular mem- 

 brane is a median floating sclerite capping the larger 

 part of the end of the cavity of the foot and which 

 bears the tactile spines extending forward below the 

 claws. This floating sclerite in other insects forms the 

 base of the empodium and pulvillae. Neither of these is 

 present in the case of the plant lice unless the soft skin 

 immediately beyond this sclerite be so designated. The 

 lower edge of the margin of the cavity is a strongly 

 developed ridge upon which the internal tendon bears 

 when the claws are extended, and against which the float- 

 ing sclerite rests in extreme flexion. On either side of 

 this thickened and elevated ridge there is a distinct notch 

 allowing considerable lateral motion of the sclerite. The 

 posterior ridge of this floating sclerite extends inward 

 as two processes joining with the two wings of the heart- 

 shaped tendon. The tendon proper is entirely internal 

 as is shown in the figure, and the muscle fibers are 

 attached to all sides. The other attachment of the muscle 

 is to the base of this large second joint of the tarsus. 



There are really no true tendons in insects; t. e., the 

 tendons of the legs are only such in a physiological or 

 morphological sense, and not at all in structure or origin, 

 but belong instead to the class of internal processes which 

 includes the well-known internal skeleton or the head and 

 thorax, the tendons of the jaws in mandibulate insects, 

 the great internal disk-like tendons for the attachment of 

 the elevator muscles of the wings in the Odonata, and the 

 skeletal and tendonal process of the ovipositor. The 



