138 



VIEWS OP THE MICROSCOPIC WORLD. 

 Fig. 233. 



Fig. 232. 



of a spiral thread is seen at a, the thickness of which measures only one-fifteen 

 thousandth part of an inch. The breathing tubes, with the branches into which 

 they subdivide, are very numerous in some insects, amounting to more than 

 eighteen hundred, and the ramifications become at length so exquisitely fine, 

 that the most powerful lenses fail to detect them. 



MAGNIFIED FLEA. This wonderfully active little creature, is delineated in draw- 

 ing 237, as it appears under a moderately magnifying power. The head (1) is 

 small, and covered with a shelly plate, and on either side gleams a brilliantly 

 dark eye, (2) the pupil of which is encircled with an iris of a greenish hue. Be- 



