- 218 | Transactions. 
into the tibia without any modification. The origin of the organ, in this 
family, was probably a simple notch or ridge on the tibia; this developed 
into a fold, and thence into a flap, after which, in some instances, it 
narrowed into a spur-like form. The walls of the strigil are not fused, and 
can be separated without difficulty. In Porina the strigil is strongly con- 
cave to the tibia, forming a rounded channel for the reception of the 
antenna (Plate 18, fig. 3). The outer sinus is not usually produced far 
The antennae of this species are very short 
ort. 
and but slightly hairy, and both tibia ánd tarsi bear thick spreading tufts 
is of the usual generic type, though rather small, while in the female it is 
reduced to a mere vestige (fig. 8). The tibia, beneath the strigil, is 
covered with curved macrotrichia, and these are still present forward of 
the diminished female organ. It seems probable that these hooks form 
the essential part of the cleaning-apparatus, that the strigil is now more 
or less functionless, and is undergoing reduction accordingly. 
Suborder HETERONEURA. 
_ In the Heteroneura the typical strigil is a rather flat organ, something 
like a longitudinally folded leaf. In t i і 
central, leaving a considerable portion of the inner part single, but in the 
higher groups the folding is often complete, and the strigil tends to become 
irregularly tubular. The structure is more or less convex to the limb, а 
18 clothed on the inner side with short dense hair. It is situated on the 
lower surface of the tibia, and usually takes an outwardly-oblique course. 
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from near the base and extend to the apex; in the Pterophoridae, where 
position. The tibia itself is usually flattened beneath, and the hair on 
that part of its surface 
strigil, and apparently aets as p > th 
e pero part of the cleaning-apparatus. Benea 
the strigil the tibia is often hollowed out so as va dep. groove for th 
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