EXTERNAL STRUCTURE OF INSECTS. 39 



beautiful, and perhaps the most strikingly so is the fringe- 

 guarded spiracle of the large water-beetle (Dyticus). The 

 reader may easily prepare this for examination by simply 

 cutting through the skin under the wing-cases, removing 

 the part containing the spiracle and washing it well with 

 water and a camel-hair brush. The two pairs of 

 breathing holes nearest to the tail are the largest and 

 most beautiful. 



