MOTIONS OF INSECTS. 275 
tion, glide along so slowly upon the ground as to be a 
quarter of an hour in going the breadth of the hand 
whence the natives call their bands Gards-drag #2 
As a further help, others again call in the assistance 
of their unguiform mandibles. These, which are pe- 
culiar to grubs with a variable membranaceous head, 
especially those of the fly tribe (Muscide), when the 
animal does not use them, are retracted not only within 
the head, but even within the segments behind it; but 
when it is moving they are protruded, and lay hold of 
the surface on which it is placed. ‘They were long ago 
noticed by the accurate Ray. ‘This blackness in the 
head,” says he, speaking of the maggot of the common 
flesh-fly, ‘is caused by two black spines or hooks, 
which when in motion it puts forth, and fixing them 
in the ground, so drags along its body *.”—The larvee 
of the aphidivorous flies (Syrphus, I’.), the ravages of 
which amongst the Aphides I have before described to 
you’, transport themselves from place to place in the 
same way, walking by means of their teeth. Fixing 
their hind part to the substances on which they are 
moving, they give their body its greatest possible ten- 
sion; and, if I may so speak, thus take as long a step 
as they can: next, laying hold of it with their mandi- 
bles, by setting free the tail and relaxing the tension, 
the former is brought near the head. ‘Thus the animal 
proceeds, and thus will even walk upon glass*. Some 
grubs, as the lesser house-fly (Musca domestica minor, 
De Geer), have only one of these claw-teeth; and in 
4 De Geer, vi. 338. > Tbid. vi. 65, © Mist. Ins. 270, 
“Vor. I. 4th Ed. 264. ¢ Reaumur, ui. 369, 
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