INSECTS : THEIE BEEATHING OEGANS. 113 



sieve, wliicli the finest atoms of dust cannot pene- 

 trate. 



The same end is attained, in another way, in the 

 dirty cylindrical grub, which is found so abundantly at 

 the roots of grass in pasture lands, and which country 

 folk call, from the toughness of its skin, " leather-coat." 

 It is the larva of the Crane-fly {Tipula oleracea), so 

 familiar to us under the soubriquet of Daddy Long-legs. 

 I can easily procure one of these, for, unfortunately, 

 they are but too ubiquitous. Here is one, who shall 

 have the honour of being martyred for the benefit 

 of science. Before we assassinate him, however, just 

 look here, at the hinder extremity of his body, Avhere 

 there is an area, surrounded and protected by several 

 points, and in this area, two black spots. 



With the dissecting-scissors I have carefully cut out 

 one of these specks, and now I put it under the Lieber- 

 kuhn, for illumination on the stage of the microscope. 

 There is, first of all, a dark homy ring of an oval figure, 

 a little way within which there is an opaque, dark plate 

 of the same figure, but smaller, occupying the central 

 portion of the area. The space between the margin of 

 the plate and the bounding ring is occupied by a series 

 of slender filaments, placed side by side, proceeding 

 from one to the other, through the interstices of which 

 the air is filtered. The central plate seems to be quite 

 imperforate. 



The fat, thick-bodied grubs of those beetles called 

 chafers, exhibit, in their spiracles, a modification of this 

 strnctui-e, rendered still more elaborate. In the case 

 of the larva of the common Cockchafer {Melolontha 

 vulgaris), fov example, the central plate is a projection 

 from one side of the margin of the spiracle — to use a 



