244 ANIMALS AT WORK AND PL A Y 



others occupy shells like miniature bivalves, others 

 are forms of the one-eyed microscopic monster of the 

 ponds, the Cyclops. All are of prodigious fecundity, 

 and proof against astonishing changes of temperature, 

 and the eggs and young, the microscopic offspring 

 of the water-midgets, pervade every drop of the 

 surface ocean, the rivers, and the ponds. In fresh 

 water the common water-fleas often discolour a pool ; 

 they produce three broods a month, with forty or 

 fifty eggs in a brood ; other species swarm on the 

 leaves of every water growth, and adhere to every 

 filament of the fuci and conferva. The Cyclops will, 

 it is calculated, beget four hundred and forty-two 

 thousand young in the course of a year ; and the 

 Cetochilus, or ' whale-food/ is said, even in the Firth 

 of Forth, to form almost exclusively the food of 

 the herrings and the sea-living salmon and salmon- 

 trout. Their existence is one of the greatest economic 

 triumphs of nature. They are the creatures which 

 dispose of the refuse of the world in the sea, and 

 keep it sweet. Dead vegetable and animal matter 

 feed these entomostraca, and they are converted with- 

 out further machinery into the food-fishes of the 

 world, or at one remove, when these are eaten as 

 food by other fish, such as the tunny, the cod and the 

 mackerel, which follow the herring-shoals. Nothing 

 short of assimilation in the digestive organs of fish 



