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flies, compared with the area of their pulvilli, both of the membranous portions and of the surface covered by the organs of holding, show the following

curious facts. That atmospheric pressure, if the area of the flaps be alone considered, is equal to just one-half the weight of a fly. If the area covered by the tenet hairs be added, an increase of pressure is gained, equal to about one-fourth the weight of a fly. This still leaves one-fourth to be accounted for, by slight viscidity of the fluid, by the action, which may be called 'grasping,' by molecular attraction, and doubtless, by other agents still more subtle, with which we have at present scarcely any acquaintance."

We give also a figure of a group of "tenet hairs," from a species of Beetle (Pterostichus niger) in which these appendages are unusually large; from which we may predicate of the character of the minute hairs on the pad of the fly, to which these are doubtless analogous.

In addition to what I have communicated on a former occasion, I desire to make a few further observations on Spiracles, which, I trust, may not be without interest to some.

The possession of a mounted spiracle of the larva of the fly is desirable to the microscopist who takes an interest in insect structure, and the questions naturally arise, how is the larva to be obtained? and where are its spiracles situated?

Kirby and Spence say, "The larva of the fly is a disgusting grub, without wings, without legs, without eyes, wallowing well pleased in the midst of a mass of excrement." This statement would seem rather to repel them invite the attention, and few indeed would feel inclined to disturb the larva's enjoyment of its peculiar haunts, yet it may be readily obtained by the most sensitive, and interest may be excited, and instruction may be obtained by its dissection, and that quite free from any feeling but the pleasure and admiration which generally attend the lover of Nature in his investigations. One day I placed a dead mouse on a shelf, with the intention of mounting some of its hair, and while I was making the necessary preparations, a blow-fly lighted upon it, and deposited a few eggs on its mouth. When I had taken the hair I required, I covered the mouse with a glass shade, with the intention of watching the progress of the eggs, and not to say anything about this, suffice it to state that after a few days, I had many specimens of veritable, full grown larvæ. I searched for the spiracles in one of these, expecting to find them along the sides, where they are usually found in the larvæ of moths, but I soon saw they were not there, but that they appeared as two brownish specks in one end (fig. 1), from

which two tracheæ stretched through the body from end to end.

They were easily mounted, as they required but little cleaning, and little steeping in turpentine, the chie thing to be attended to, being the prevention

of particles of dirt from entering the spiracles, as it would be difficult to get rid of these by the most careful washing.

In bees, wasps, &c., the spiracles of the abdomen