THE TRACHEA. 



naturalists have agreed upon the short formula which 

 has already been given. 



It is there stated that insects breathe through 

 ' tracheae.' Now tracheae are tubes composed of thin 

 membranes, kept open by a fine but stiff wiry thread, 

 which is twisted spirally throughout the whole course 

 of the tube, just as a modern flexible gas-tube is kept 

 open by a spiral wire, no matter how it may be twisted 

 or bent. This is absolutely necessary in insects, for 

 the tracheae are not confined to a single portion of the 

 body, like the lungs of men or the gills of fish, but 

 permeate the entire insect, passing through all the 

 limbs, and even reaching to the claws which terminate 

 the feet. Any of my readers who wish to see the 

 extraordinary manner in which the breathing appa- 

 ratus is disposed over the whole body should look at 

 the plates of Strauss Durckheim's wonderful mono- 

 graph on the common cockchafer, a work to praise 

 which would be simply impertinent. 



I strongly advise all my readers to examine these 

 marvellous structures for themselves. There is not 

 the least difficulty in finding them, for the real diffi- 

 culty is to dissect any part of the body without finding 

 them. The largest of these tubes are those which 

 run along the sides of the insect, and are connected 

 with the oval openings along the sides, which are 

 possessed by every insect. These openings are called 

 spiracles, from the Latin word spiro, because through 

 them the insect breathes. Any insect or caterpillar 

 w r ill furnish the tracheae, but the larger the better. 

 They should be severed from the body by a pair of 

 fine scissors, then taken out with a pair of forceps, and 



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