42 ON ENTOMOLOGY. 



bute to the preservation of its claws, whose pointed extremities would 

 soon be impaired without this prevention. Its ability to walk on glass, 

 says Shaw, proceeds partly from some little ruggedness thereon, but 

 chiefly from a tarnish or dirty smoky substance adhering to the surface ; 

 so that though the sharp points on the sponges cannot penetrate the sur- 

 face of the glass, it may easily catch hold of the tarnish. This is evi- 

 dently borrowed from Hook ; but it is singular that none of these fanciers 

 ever took the trouble to ascertain the existence of either a gluten 

 squeezed out by the Fiy, or of the smoky tarnish on glass. Even the 

 shrewd Reaumur could not give a satisfactory explanation of the cir- 

 cumstance. 



The earliest correct notion of this curious subject was entertained by 

 Derham, who, upon mentioning the provision made for insects that hang 

 on smooth surfaces, says, I might here name divers Flies and other in- 

 sects who, besides their sharp hooked nails, have also skinny palms to 

 their feet, to enable them to stick to glass and other smooth bodies by 

 means of the pressure of the atmosphere, after the manner as I have seen 

 boys carry heavy stones with only a wet piece of leather clapped on the 

 top of the stone. The justly celebrated Mr. White, of Selborne, appa- 

 rently without the aid of microscopical investigation, adopted Derham's 

 opinion, adding the interesting illustration, that in the decline of the year, 

 when the Flies crowd to windows and become sluggish and torpid, they 

 are scarcely able to lift their legs, which seem glued to the glass, where 

 many actually stick till they die j whereas they are during warm weather 

 so brisk and alert that they easily overcome the pressure of the atmo- 

 sphere. The apparatus in the feet of the Fly consists of two or three 

 membraneous suckers, connected with the last joint of the foot by a 

 narrow neck, of a funnel shape, immediately under the base of each 

 claw, and moveable in all directions. The suckers are covered above 

 and hollow below the edges, being margined with minute serratures, 

 and the hollow portion covered with down. In order to produce the 

 vacuum and the pressure, these membranes are separated and expanded, 

 and when the Fly is about to lift its foot, it brings them together and 

 folds them up as it were between the two claws. By means of a com- 

 mon microscope these interesting movements may be observed when a 

 Fly is confined in a wine glass. 



The CHEQUERED BLOW FLY (Sarcophaga Carnaria) hatches its eggs in an 

 abdominal pouch, and instead of eggs, depositing maggots upon dead 

 carcases. The eggs of all Flesh Flies are in sultry weather hatched with 

 great rapidity ; but in the case of the Chequered Blow Fly, nature has pro- 

 vided the means of still more rapid destruction for removing the offen- 

 sive part of carcases. The arrangement of the numerous minute larvce 

 in the pouch is very remarkable, and resembles the coil of a watch- 

 spring, or a roll of ribbon. Reaumur had the patience and perseverance 

 to uncoil the multitudinous assemblage of Flies in embryo, and found it 

 about two inches and a half in length, though the body of the Mother 



