INSECTS : THEIR BREATHING ORGANS. 



99 



Various and beautiful are the modes in which this 

 common purpose is effected, but I can show you only two 

 or three. This is one of the breathing orifices of the 

 common House-fly, in which, as you see, minute processes 

 grow from the margin all round, which extend partly 

 across the open area, branching and ramifying again and 

 again, and spreading and interlacing with those of the 

 opposite side, so as to form a perfect sieve, which the 

 linest atoms of dust cannot penetrate. 



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 sobriquet of Daddy Long-legs. I can easily 

 procure one of these, for, unfortunately, they are but too 

 common. 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, where there is a space, 

 surrounded and protected by 

 several points, and in this 

 space, two black spots. 



With the dissecting-scissors 

 I have carefully cut out one 

 of these specks, and now I put 

 it for illumination on the stage 

 of the microscope. There is, 

 first of all, a dark horny 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, 

 margin of the plate and the bounding ring is occupied 

 by a series of slender filaments, placed side by side, 



ii 2 



SPIRACLE OF LEATHEU-COAT. 



The space between the 



