1921] Uichanco — Movement of Tarsi in ApliiJs 67 



liinge, the tarsus is stretched medially and becomes extended so 

 as to bring it at an approximately straight line Avith the tibia. 

 Relaxation of the extensor removes the force which pulls the first 

 tarsal segment at the place indicated, and tlie tension of the wall 

 of the tibia brings the former back to its original position. It 

 appears, therefore, that the wall of the tibia performs the function 

 of the lost antagonistic muscle of the tarsi in aphids. The move- 

 ment of the tarsi in either direction is limited by the articular 

 membrane. 



As has already l)een noted, the movement of the second tarsal 

 segment is ai^parently very restricted, pro'xibly to the extent of 

 merely giving the tarsus a certain amount of resiliency when the 

 insect is walking. It has not been observed in the present Avork 

 to ilex to any marked extent either ectally or entally with respect 

 to the first tarsal segment. 



Summary. 



In certain more primitive insects, two antagonistic muscles move 

 the tarsus. In the aphids, one of these is lost through degenera- 

 tion or atrophy, only the extensor remaining. 



The function of the lost antagonistic muscle is taken over by 

 the walls of the tibia, which, l)y its tension, has the tendency to 

 flex the tarsus outward at an angle with the tibia. 



The tarsus moves on a single hinge, located at the ectal portion 

 of the articulation of the first tarsal segment with the tibia. 



The articular meml)rane limits the movements of the tarsus in 

 either direction. 



The second tarsal segment is apparently very restricted in its 

 movement, perhaps to the extent of only giving the tarsus a cer- 

 tain amount of resiliency when the insect is in motion. 



LiTERxVruKE Cited. 

 MiALL, L. C, AXD Denny, A. 1886. The Structure and Life 



History of the Cockroach (Periplanefa orientnlis) : 77. Fig. 



37. London and Leeds. 

 WOODWORTH, C. W. 1908. The Leg Tendons of Insects. The 



American N"aturalist, 42 : -152-456, 



