The Feet of Insects. 395 



FOOT OF THE FLY. 



To study this part of our most common insect, and enter into 

 the detail of its mechanism, we should possess a microscope of 

 moderate power, and some prepared legs of either the Scato- 

 phagies, or dung- fly, ovMusca vomitoris, or flesh-fly, and with a 

 low power look at it as a whole. The tarsal joints are five, in 

 all the Diptera ; terminated in the fly by two black, strong claws 

 and two Pulvilli, or white semi-transparent lobes, which are 

 expansions of a membrane like parchment, apparently delicately 

 fringed (fig. 1). These were formerly supposed to be suckers 

 moveable in all directions, with a downy, convex surface and 

 finely- granulated concave surface, which, being pressed closely 

 to the plane of position, the air was supposed to be sufficiently 

 expelled to produce the adhesion necessary to keep the fly from 

 falling when walking upon glass, wall, or ceiling; the suckers 

 contracting and dilating according to necessity. 



Improvement in microscopes and a habit of careful investi- 

 gation have led to a further discovery, first by Mr. Blackwall,* 

 and then by Mr. Hepworth,* which proves this supposition to 

 be an^erroneous one. 



They have ascertained that the delicate fringe of hair is 

 itself the point of attachment, each hair being a minute tube, 

 expanding at the tip into a disk or sucker, through which flows 

 a viscid fluid, by means of which the fly's foot is attached to 

 any dry surface so firmly as to require the action of those two 

 strong claws to detach it again (fig. 1 a) . 



It was but a few days ago that I noticed a small house-fly 

 jerking in a queer way upon the glass, as if in a fit of St. 

 Vitus 5 s dance, pulling up first one leg and then the other, but 

 evidently unable to walk or detach itself from the glass. Upon 

 a closer examination with a pocket-lens I saw from the appear- 

 ance of certain white rings round the abdomen that the fly was 

 really " very poorly," attacked with Bmpusa Muscee — a disease 

 to which they are very subject at this time of the year. This is 

 an inward malady, arising from the growth of a fungus, which 

 eventually consumes the whole viscera, and, doubtless, the 

 muscles also, then breaks forth between the segments of the 

 body, and the fly is seen sticking to the glass, surrounded by a 

 halo of white dust — the spores of this fungus. The fly I was 

 observing, weakened, doubtless, by the loss of some muscles_, 

 and the fluid continuing to flow from its suckers, it had no 

 strength to contend with it. 



The muscular power needful for the action of the claws must 

 be considerable, when it is remembered that some flies run with 

 such swiftness as to take 5i0 steps in a demi-second — equal to 

 * Quarterly Journal of Microscopic Science, 1854, vol. ii. p. 158. 



