THE SPRING BROOK 193 
silt on the pool-beds; worms, by planarians 
gliding over the stones of the bottom, and by 
Tubtfex, in tubes in the bottom mud, waving 
their long, lithe, filamentous, red bodies in the 
water; andinsects, 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 burrowers in the 
bottom. The spring brook does not harbor 
mosquitoes, but horse-fly larve (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 
BIG Ts spine brook are few, and many of them are so 
pebiting &l8- restricted by conditions that, wherever they 
lerpes) 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.”: 
Fic. 76. A caddis-worm (Phryganea), 
“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.” 
Fic. 77. A horse-fly larva. 
