MR. TUFFEN WEST ON THE FOOT OF THE FLY. 395 



clear for the admission of light, it requires to be constantly removed. To opticians, a 

 similar deposition of moisture on the glasses of their lenses is but too well known ; they 

 call it the "sweating of glass." 



Hooke clearly foresaw the difficulties presented by the "viscid secretion" theory, and 

 put them in the following forcible manner : " I could not well comprehend how, if there 

 were such a glutinous matter in those supposed sponges, as most (that have observed that 

 object " [the Fly's cushions] " in a Microscope) have hitherto believ'd, how, I say, the 

 Fly could so readily unglew and loosen its feet." 



Leeuwenhoek {circa 1690)* brought to this, as he did to every other subject he investi- 

 gated, his usual clear-headed sagaciousness. He saw flies, " almost as large as a bee," 



" every year " "in the month of August, sitting on a glass, at the backside 



of " . . . "his house" (Uristalis tenax). "The extremities of their feet," he found, "were 

 covered with an incredible number of hairy parts, by the help of which they are better able 

 than other flies to climb up a glass though it be ever so free from impurities or irregularities 

 of which they might take hold. I have therefore," he says, " often placed the feet of those 

 flies before the microscope, in order to view the means by which they can fasten themselves 

 to the glass, and run up it ; and I have for some years past thoiight that I could discover 

 that these hairs were each of them provided with crooked parts like hooks, by the help of 

 which they can take the firmer hold on glass ; but which parts have never, to my know- 

 ledge, been described by any person, though the figiires of those hairs may be seen in 

 many authors." 



Here there is a distinct reference to the peculiar flexure downwards of these parts, 

 which will presently have to be mentioned in the description that I shall give of them 

 from my own observations. 



Leeuwenhoek, thinking that the action of these hairs was purely mechanical (/. e. that 

 +.hey acted only like so many minute hooks), illustrated his views by a description, which 

 follows the above, of his observations on some remarkable hairs on "the hind-feet" of 

 " laro-e crabs "...." caught among the rocks in Norway ;" which hairs are " many of them 

 provided with a double row of parts like teeth, placed in very exact order beside each other, 

 in like manner as if we were to imagine the back of a knife cut into a double rovv^ of teeth or 

 notches." "This wonderful formation, I am persuaded, is intended for this pur- 

 pose, that when the crab is climbing up the rocks, he may be enabled by this assistance 

 to fix his feet firmly on the rocks or stones f." 



He also describes another form of insect-foot which bears distinctly on our present 

 purpose, in the notice of a "Fly" infesting " the blossoms of fruit-trees, particularly 

 apples " {Anthonomns 2^omorum ?). " Observing," he says, " that these insects " could run 

 along or stand for a long time on any side of the glass, even with their feet upwards, I was 

 desirous to examine accurately the formation of their feet, and, in tliis little creature, I saw 

 such perfectly formed limbs, enabling it to adhere to the glass, and to run along upon its 

 surface, as distinctly as I had ever seen in other larger flying animals." 



* Collected Works (translated by Samuel Iloole, 1800-1807), vol. ii. part 3. p. "1. 

 t Ibid. pp. 71, 72. 

 VOL. XXITI. 3 II 



