254 



SCIENOE-GOSSIP. 



[Nov. 1, 186S. 



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 

 tenent 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 

 maybe 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 " tenent 

 hairs," from a species of Beetle {PterosticKus 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. 



SPIRACLES OF INSECTS. 



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. 



Tiie 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, with- 

 out eyes, wallowing well pleased in the midst of a 

 mass of excrement." This statement would seem 

 rather to repel than invite the attention, and few 

 indeed would feel inclined to disturb the larva's en- 

 joyment 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 dis- 

 section, 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 inten- 

 tion of watching the progress of the eggs, and not to 

 say anything about this, sufiice it to state that after 

 a few days, I had many specimens of veritable, full 

 gi'own larvae. I searched for the spiracles in one of 

 these, expecting to find them along the sides, where 

 they are usually found in the larvae of moths, but I 

 soon saw they were not there, but that they appeared 

 as two brownish specks in one end (fig. 1), from 



Fig. 1. Spiracles of Larva of Fly. 



which two tracheae 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 



/ 



Fig. 2. Tenninal Spiracle of Bytiscus. 



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 



