142 



Marvels of Insect Lite, 



obvious reason being the exclusion of dust and other minute foreign matter from 

 the air-tubes. In the beetles they are covered by the edges of the wing-covers. 



As the body contracts in respiration the spiracles open ; when it expands the 

 spiracles are closed and the air forced by muscular pressure into the remotest 

 ramifications of the finest air-tubes. In flying Insects the air-tubes expand at 

 intervals into oval, elliptical, or pear-shaped sacs, which, of course, afford a much 

 larger supply of air than the air-tubes alone, and so increase the breathing capacity 

 necessitated by the greater muscular exertion. A former explanation was that 

 the body was lightened by the extra amount of air in it ; but this is now known to 

 be incorrect, its specific gravity in air not being affected. 



Bacon-Beetles. 



Sir Edward Coke, the great sixteenth-century lawyer, has declared that " the 

 house of every one is to him as his castle and fortress, as well for his defence against 

 injury and violence, as for his repose." But although we are all fond at times of 

 boastfully expressing ourselves in the spirit of this legal aphorism, we know that 

 except against the enemies and annoyers that are of our own kind our strong walls 

 and locks are incapable of defending us or ensuring our repose. Numerous enemies 



Photo by] 



Air-tubes of the Silkworm. 



[/. F. IIcinuniiHil. 



A portion of one of the triiiikliiics seen in a previous photograpli is lierc shown niagnificcl twelve times. It will be seen tliat 

 at intervals agreeing with the breathing months a nnmber of branch tubes are given off. These convey air to those parts of the 

 silkworm distant from the sides. 



