INSECTS 



163 



count of the great numbers of species concerned. There- 

 fore it may well be postponed until after we know more 

 of the life of some of the more familiar and interesting 

 insects. A good way to begin the study of systematic 

 entomology is to make a collection of insects of all kinds. 

 Directions for collecting and preserving insects are given 

 in Appendix B. The best book of insect classification is 

 Comstock's "Manual of Insects." 



Pond and brook insects. — There is space in this book 

 to take up but few of the many interesting insects which 

 can be readily found and observed. Among the most 

 available are the common pond 

 and brook insects. Land insects 

 live under most diverse conditions, 

 that is, on the ground, in the 

 leaves, fruits, and stems of plants, 

 in the trunks of trees, or in dead 

 wood, in the soil, in decaying 

 animal or plant matter, and as 

 parasites on or in other animals, 

 but the aquatic kinds are almost 

 wholly limited to fresh water. A 

 few species live on the surface of 

 the ocean, however, and a few 

 others on the water-drenched rocks 

 and seaweeds between tide-lines. 



On the under side of stones, in 

 brook "riffles," and in pools and 



Fig. 119. — \oung (nymph) of 



watering-troughs not too frequently Mayfly, showing (g) tra- 

 used are to be found commonly cheai gills. (From Jenkins 



and Kellogg.) 



the young, i.e., nymphs (fig. 119), 



of Mayflies, recognizable by the rapidly vibrating flap- 

 like tracheal gills along each side of the flattened delicate 

 body, three pairs of legs, and two or three long, slender 

 filaments projecting from the tip of the abdomen. Those 



