156 ZOOLOGY 



in a rich soup of smaller green organisms upon which they can 

 feed, they multiply enormousl)-. As many as 20,000 of the 

 adults of one species of Copepod have been counted in one 

 cubic meter of sea water, and of larval Entomostraca, nearly 

 200,000. And the total volmne of the Entomostraca of the 

 ocean, if brought together, would make a conical hill about 

 12 kilometres in diameter and 300 metres high. The 

 Entromostraca of the sea if driven into Long Island Sound, 

 which is 80 miles long and 10 miles wide, would fill it full from 

 the bottom to the present sea-level, leaving no room for water, 

 and this vast Imlk of organisms is frecjuently renewed. 



This enormous mass of Entomostraca is made availal)le 

 for man, since it forms the principal food of many edible fishes. 

 As the fish swims through the sea near the surface it opens its 

 mouth anrl lets the water flow into it and out at the sides 

 through the gills. In jjassing out the small sohd particles 

 are strained from the water by the gill-rakers and are then 

 swallowed. As the young fish feed they grow, and so the 

 Entom.ostraca are transformed into f(5od for man. 



The gToup of Entomostraca includes a great ^'ariety of or- 

 ganisms which are all of small size with a varialile nvmil)er of 

 body segments and appendages. There are five orders which 

 we will next consider. 



The fairy shrimps or Branch'iopoda ' include long, mostly 

 macroscopic organisms with 10 to 40 jiairs of legs. The legs 

 are leaf-like and serve lioth as paddles and as lireathing organs. 

 These animals are found in the spring in pools that dry up 

 later in the year. They produce eggs which have such thick 

 shells that they can withstand drj'ing for a year or even several 

 years ; indeed they will not hatch until they have been dried. 



1 Latin, l>raiichiuni, gill ; Greek, pous, foot. 



