94 A NATURALIST IN THE GREAT LAKES REGION 



the bottom of the pond. When it dries up they dry, too. 

 They may blow about in the wind to new locations. They 

 freeze with the winter cold; in fact they will not hatch until 

 they have dried out and frozen. And so they are ready to 

 start the next generation in the ponds of the following 

 spring. 



Other inhabitants of these ponds are the red water mite, 

 Hydrachna; a tiny crustacean with a bivalve shell, looking like 

 a very small clam until it sticks out its feathery swimming 

 organs (Cypris marginata) (Fig. 56^) ; the water sow bug (Fig. 

 560); the bender (Fig. 566), a crustacean that swims rapidly 

 with even speed, but which when taken in the hand bends and 

 unbends rapidly; Cyclops, Daphnia (Fig. 56 /, h); some clado- 

 cerans; the green flat worm. Here, too, one may find, if low 

 prairie is near, the spring peeper, Chorophilus nigritus, that 

 marsh tree frog whose clear peep is almost like a bird note. 

 It takes to the ponds to lay its eggs almost before the ice is gone. 

 The eggs are laid in gelatinous clusters that fill the palm of the 

 hand and in the pond are attached to the grasses along the 

 margins or to sticks in the shallow places. 



The frog's egg is admirably adapted to hatch on these cold 

 days. It is covered with a transparent jelly layer that retains 

 the sun's heat like the glass of a greenhouse. It has a black 

 upper surface that absorbs heat like a black dress. The egg is 

 laid so early that it avoids many of the insect larvae that would 

 later prey upon it. It is inconspicuous, its black upper surface 

 harmonizing well with the dark pond bottom when seen from 

 above, and its light under surface with the clouds when seen from 

 below, so that it easily escapes detection. 



Just as there are an early spring flora in the woods and a 

 spring fauna in the temporary ponds, so there are early spring 

 plants and animals in the swamps, on the dunes and in other 

 typical localities. In each place the spring types are followed 

 by early summer types, by midsummer and autumnal species. 

 One need only call attention to this seasonal distribution to have 



