66 Psyche [June 



A short tendon-^ connects it with the projection of the tarsus. The 

 tendon Avhich connects this nuiscle with the subproxinial end of the 

 til)ia is relatively much longer and narrowly subfusiform, abruptly 

 expanding sul)conically toward the point of origin. 



It is of considerable interest in connection with the musculature 

 of the tarsi in aphids that the flexor is absent, its function having 

 heen taken over by another arrangement which will be described 

 presently. In the more primitive types of insects, as in the Blat- 

 tidse, two antagonistic sets of tarsal muscles are present. Miall 

 and Denny (1886) found a flexor and a retractor moving the tarsi 

 of Blatta orientalis Linn. The disappearance of the flexor tarsi 

 in aphids must have been the result of degeneration consequent 

 upon the more highly specialized habits of this insect. 



The junction between tlie iirst and the second tarsal segments 

 has not been satisfactorily studied in connection with the present 

 work. It api)ears. however, that the two segments are more or 

 less firmly connected by a narrow strip of articular membrane in 

 such a way as to give the second tarsal segment only a very restricted 

 amount of independent movement. 



Mechanism of Tarsal ]\Iovement. 

 From an examination of the anatomical structure of the legs, as 

 well as from direct study of their movements under the microscope, 

 it is evident that movement in the tarsal region centers around the 

 flrst tarsal segment. Apparently, the tension of the highly chitin- 

 ized wall of the tibia has the tendency to stretch the articular 

 meml)rane outward, and, since the single hinge is located at the 

 ectal part of the articulation of the first tarsal segment with the 

 tibia, where it offers resistance to the tension of the tilnal wall, 

 the tarsus is bent on this hinge at an angle of about 90 degrees. 

 As the extensor tarsi contracts, an upward ])ull is applied on the 

 entoproximal margin of the first tarsal segment. Pivoted on the 



^' The term tendon, as used in the present paper, is applied to the more or 

 less subcylindrical strand of tissue which connects the main body of the 

 muscle with the inner wall of the insect's legs. As used by Woodworth 

 (1908), the word apparently has a different significance. So far as I was 

 able to make out from both his discussion and his figures, it is apparently 

 meant by him to apply to the projection or elongation of the chitinous wall 

 which serves as the muscular insertion. 



