THE SPRING BROOK 



193 



silt on the pool-beds; worms, by planarians 

 gliding over the stones of the bottom, and by 

 Tubifex, in tubes in the bottom mud, waving 

 their long, lithe, filamentous, red bodies in the 

 water; and insects, by a number of inhabitants 

 of the submerged vegetation caddis-worms 

 (fig. 76), mayfly nymphs (fig. 23), midge larvae 

 (fig. 24), etc., and by a few burro wers in the 

 bottom. The spring brook does not harbor 

 mosquitoes, but horse-fly larvae (fig. 77) live in 

 the soft bottom and emerge in midsummer 

 to annoy farm animals. 



As compared with the population of warm 

 and stagnant pools, the denizens of the spring 



P mon 5 ' .spring -! brook are few, and many of them are so 

 restricted by conditions that, wherever they 

 are found, they serve as an indication that the 



water is pure and cool and permanent. The spring brook 



sustains the life of 



these, and helps sus- 

 tain innumerable 



others that come and 



go, or that dwell 



about its borders. Bryant has sensed this in his "Forest 



Hymn.": 



"Yon clear spring, that, midst its herbs, 

 Wells softly forth and visits the strong roots 

 Of half the mighty forest, tells no tale 

 Of all the good it does." 



ma b tide n r g 



FIG. 76. A caddis- worm (Phryganea). 



FIG. 77. A horse-fly larva. 



