1932 ] 
Tibial Muscles of Aphids 
65 
determine the presence of a proximal elongation of the first 
tarsal segment, for the insertion of the extensor muscle, as 
described by Uichanco. The extensor muscle is inserted 
directly on the endo-proximal edge of the first tarsal seg- 
ment as may be seen in the drawings. In some cases 
(Fig. F) this muscle arises on the proximal end of the 
tibia, where there are two points of origin, one on the endo- 
proximal, and the other on the ecto-proximal wall of the 
segment. From this origin the muscle passes outward 
through the segment as a very thin tendon-like muscle. 
Just before the insertion on the tarsus, however, this muscle 
becomes very wide and again abruptly narrows down into 
a tendonous insertion on the first tarsal segment. (Figs. 
A, G.) This muscle is called the extensor by Uichanco. 
A second muscle (extensor) appearing in the species 
studied, is very short and much wider than the first muscle 
mentioned. This one arises on the lateral wall of the tibia, 
slightly distad from a point midway between the proximal 
and distal ends of the segment. From this origin, which is 
rather wide, the muscle passes out to the tendon-like inser- 
tion on the endo-proximal edge of the first tarsal segment. 
The combination of the above mentioned muscles has been 
observed in Colopha ulmicola, Aphis rumicis and Ampho- 
rophora cosmopolitania. (Figs. A. D.) In some cases the 
extensor muscle which arises in the proximal end of the 
tibia is absent. In this case a short muscle, similar to the 
second extensor muscle mentioned, replaces it. This is found 
in Aphis sambucifolii, Drepanaphis acerifolii and Aphis 
feminea. (Figs. B, H.) A further variation is found in the 
muscles of Eriosoma lanigerum . Here there are four small 
extensor muscles. (Fig. E.) 
The function of the missing flexor muscle is taken over 
by “the tension of the wall of the tibia.” 1 The fulcrum 
upon which the tarsus moves is located at the ecto-distal end 
of the tibia. (Fig. G.) The first tarsal segment increases 
slightly in width from the proximal to the distal end. When 
the extensor muscle contracts, it draws the first segment of 
the tarsus into the cavity of the tibia, and thus, since the 
tarsus is of slightly increasing greater width, a tension is 
1 All quotations are from Uichanco. 
