KKCIIKATIYK NA'iUiAI, m.-'J . l:Y. 





THE FOOT OF THE 

 HOUSE-FLY (MAGNI- 

 FIED). 



EECREATIVi: NATTKAL HISTORY, 

 :. iiiifs:: l-M.v. 



As the family of insect* to which tho house-fly belongs 

 n above one hundred spec. i. limit 



oiiruU.-ntu.il, in thin jniper, to that bii/./iii.^ and t< .. 



ss .luring the sultry days of summer. 

 on house-fly (Afuaca domestica) may seem too well 

 known t rc.|!iii-c any description. But thoro aro many v. 

 :in:itiun, something to wonder at in this <li)>: 

 Tim win},'-* an. 1 |> >wer of flight claim our consideration 

 first. Those who closely w:it--h will often bo Kiiqiri^ed at tho 

 manner in which tho fly moves through tho air with its bock 

 Is. Of course when the insect 

 darts from a tablo to tho ceiling it must 

 perform a kind of somersault in tho air. 

 Tho feet, which were downwards on tho 

 tablo, must be turned uppermost to grasp 

 tho ceiling. The motion is so rapid and so 

 unexpected that not one case in a thousand 

 may attract our notice. A keen watchf ul- 

 iie.--.s will also enable us to observe that this 

 insect can fly forwards or backwards with, 

 apparently, equal ease. The rate of its 

 motion is about twenty miles an hour, so 

 that a fly can compete, for some time at 

 least, with an ordinary railway train. 

 Some may here ask whether tte " buzz " 

 of the fly is produced by tho rapid vibration 

 of the wings against the air. This may, in 

 some cases, bo the cause of so peculiar a 

 sound, but no decisive answer can, with 

 our present knowledge, bo given to the question. The fly 

 is rightly called a two-winged insect, but the apparent rudi- 

 ments of a second pair can be easily seen, just behind the truo 

 wings. These singular organs aro called powers, from a sup- 

 position that they enable the fly to balance itself during its 

 rapid somersaults in tho air. These little thread-like filaments, 

 with the knob on the top of each, may remind some of the j 

 balancing-poles used by dancers on tho tight-rope. If the com- 

 mon notion respecting tho use of tho poisers bo correct, we shall 

 readily admit that the fly is well fitted for its evolutions, pos- 

 sessing both a moving and balancing apparatus. 



The feet of tho fly have long presented a puzzling problem to 

 naturalists, and some persons may even now doubt whether tho 

 action of these organs is yet clearly understood. Tho problem 

 is to explain how the fly can suspend itself from a ceiling or 

 walk up a smooth pane of glass. The " sucker " theory was 

 long popular, and we. believed, with little questioning, that tho 



1 fly's feet were supplied with a kind of air-pump, by which a 

 vacuum was produced under the feet, enabling them to cling to 

 glass much in the same manner that a boy's 

 toy sucker adheres to a stone. Let no reader 

 prepare himself to listen to a new theory on 

 tho subject ; we must content ourselves with 

 describing the successive views which have 

 been advocated, and then stating that now 

 held by those who have most closely studied 

 these fine and complex structures. Our 

 readers will bear in mind that very high and 

 clear microscopic powers, great patience, and 

 numerous observations are necessary for a 

 satisfactory examination of such minute 



" a smoky substance " noted by him on gbuis, and which be 

 tin. i/;. itlcw" in clinging to no mooth 



(surface. Wo* thix " smoky substance " the fluid observed by 

 Power, or won it uimply tho corroded face of too glans ? There 

 in no doubt that glass does undergo a decomposition, which 

 working opticians call " tho sweating." The worn and irregular 

 surface thus produced would aid an insect in clinging. Leuwen- 

 hock, tho patient and profound Dutch naturalist, employed 

 his iin]>ro\e<| microscopes in examining the " bristles " detected 

 by Dr. Hooke. Lenwenhook saw them clearly, and thought 

 that tho end of each resembled a hook. This conjecture has 

 In i-n rerifii <1 ; tho extremity of each "bristle" is cnrred, and 

 so presents a hooked form. Dr. Derham, the friend of Hooke, 

 and editor of Bay's works, 

 turned, for a time, from his 

 experiments on pendulums and 

 observations on tho solar spots, 

 to investigate tho structure of 

 a fly's foot. His researches 

 led him to adopt a notion re- 

 KemUing tho sucker theory. 

 Ho suggested that flies clung 

 to smooth surfaces by what 

 lie vaguely calls their "skinny 

 palms." Derham may have 

 had in his mind tho adhesive 

 fluid of Mr. Power and the 

 " smoky substance " of Hooke, 

 while ho himself may have in- 

 distinctly noted what aro now 

 called " tho flaps " on tho foot. 

 By combining all these, Der- 

 ham might have got his notion 

 of an adhesive cr " skinny 

 palm." Gilbert White, though 

 an acute observer of Nature, 

 was not likely to go deeply 

 in to microscopic investigations. 



THE TBUWK or THE Hocsz-n-t 

 (XAGNU-IBD). 





In 1664, Mr. Power, after long scrutiny of 

 the fly's feet, suggested that the insect clung 

 to surfaces by its hooked claws, and also by 

 the aid of a fluid poured from tubes on tho 

 feet. He saw two powers at work ; a grip- 

 ping machine in tho claws, and an adhesive action in the gummy 

 liquid. Three years later, in 1667, the Gresham professor, 

 mathematician, and naturalist, Dr. Eobert Hooke, described in 

 his " Micrographia " the "small bristles" on the " soles " of 

 the fly's feet. He called them " tenters " (holders), and counted 

 ten on each foot, thus giving to this small insect sixty holding 

 instruments. But Hooke goes on to describe what he terms 



THE ETE OF THE HOUSE-FIT 

 (MAGNIFIED). 



Diptera, a Greek word signifying " two wings." 



58y.E. 



He therefore adopted tho " sharp hooked nails " of Dr. Hooke, 

 the " skinny palms " of Derham, and the sucker theory as 

 explanatory of tho whole matter. White, however, clearly 

 admitted tho action of two powers in the fly's foot, one for sus- 

 pension, the other for producing a vacuum. Have we advanced 

 beyond this in certainty of knowledge ? Mr. John Blackwall, in 

 1830, described three conclusions to which ha hod been led. He 

 detected an expansion at tho end of each hair or " tenter," re- 

 sembling a little pad or cushion, but denied tho existence of any 

 vacuum-producer or air-pump structure. Some persons reminded 

 him that each hair, with its expanded tip, might really be a 

 separate sucker. This conclusion he refused to admit, alleging 

 it to bo unsupported by proofs. Here, then, was a distinct 

 denial, by an acute microscopic observer, of 

 tho sucker theory, accompanied, however, by 

 a clear statement that the end of each hair 

 on the fly's foot possesses a peculiar expansion, 

 looking as if it mu=t have some special work 

 to perform. Mr. Blackwall also arrived at a 

 third conclusion that a fly in walking along a 

 pane of glass leaves behind certain marks, as 

 if a fluid had been poured out at particular 

 points. He thus agrees with tho observations 

 of Power, Hooko, Derham, and White. The 

 examination was still carried on by naturalists, 

 with tho aid of the best microscopes. In 1841, 

 Mr. E. Newman called attention to the almost 

 inconceivable number of tho " bristles." 

 Hooke had estimated the whole number of the 

 " tenters " on the six feet at sixty ; Mr. 

 Newman declares they are " almost infinite." 

 This observer also saw that a liquid was poured out from some 

 part of tho complex structure. This fluid has been subjected 

 to chemical analysis, but no remarkable element has been dis- 

 covered. Water and oils appear to be the constituents, so that 

 it is similar to the ordinary matter given off by the pores of 

 tin- human skin. 



Mr. Hopworth, in 1854, observed that "the flaps" of the 

 fly's feet were trumpet-shaped, or resembling the form of a boy's 

 sucker when supporting a heavy stone. This gentleman also 





