10 MEETINGS. 



Monthly Meeting held March 13th, 1890, Mr. H. Crousaz in 



the chair. 



Mrs. Myers, Mrs. F. Rose, Miss M. Rose, Miss Chotin, and 

 Messrs. D. Corbet, F. B. Guerin, and J. J. Carey were elected 

 members of the Society. 



Mr. E. D. Marquand read a paper on " A Fly's Foot," and 

 illustrated the subject by a rough Indian ink sketch. He 

 would endeavour to give a simple and intelligible description 

 of the structure of a fly's foot — one of those marvels which 

 are seldom noticed, because they come under daily observa- 

 tion. 



The five joints composing the foot terminate in a pair of stout, 

 curved horny claws, and behind or under these there are two fleshy 

 flaps or pads. Long before the invention of the microscope it was 

 well known that atmospheric pressure acting on these flaps enabled 

 the fly to walk in any position. Gilbert White, of Selborne, a 

 century ago explained this with great simplicity and clearness. 

 Substantially the old naturalists were correct; but they fell into 

 error in supposing that each pad formed a single sucker only, whereas 

 it is a sort of cushion studded with a vast number of exceedingly 

 minute ones. Each of these minute suckers is a hollow tube broaden- 

 ing at the apex ; in fact a trumpet-shaped hair ; and at times a tiny 

 drop of viscous fluid passes down through it, which assists adhesion 

 by more effectually excluding the air. That the adhesion of a fly's 

 foot is not produced by atmospheric pressure alone is proved by the 

 fact that it will retain its position in the interior of an exhausted 

 receiver ; and that an adhesive fluid can be and is at times secreted 

 is evidenced by the marks which are left on a clear surface of glass. 

 Some have supposed that the viscous secretion is employed at all 

 times and under all circumstances; but this Mr. Marquand was 

 disposed to doubt, because it would be obviously a useless expendi- 

 ture of valuable material. The different operations he conceived 

 would be varied in this way : upon the upper surface of a horizontal 

 body or a perpendicular one offering a good foothold, like the side of 

 a table cloth for instance, the claws alone would be employed — the 

 suckers here would be evidently impediments. In ascending a 

 moderately rough, perpendicular body — say a wall or a door — the 

 pads with their suckers would be used; and upon a very smooth 

 surface, such as a window pane the additional employment of the 

 viscid seeretion from some or all of the suckers would then be 

 required. The claws (having a distinct set of muscles) are used as 

 levers in raising the pads in order to lift the foot, and the reason 

 why flies are seen in autumn adhering to walls and windows, and 

 unable to move is because an internal parasitic fungus has so 

 weakened the insect that it has not strength to detach the cushions. 

 If there were no suckers it would fall to the ground. 



The paper was thoroughly enjoyed, and a discussion 



