128 



ZOOLOGY 



minute, bean -shaped little crustaceans, which have to move 

 their appendages very vigorously to support their heavy 

 bodies in the water. The Ostracods are found in almost 

 all pools and streams,, especially in the early spring. Many 

 of them seem to be exclusively parthenogenetic. 



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V 



FIG. 119. Acartia, a marine Copopod. Greatly magnified. Photo, by 



W. H. C. P. 



Of the Copepoda 1 the commonest fresh-water genus is 

 Cyclops, which occurs in a similar habitat witli Daphnia 

 and is sometimes found even in pure drinking water. 

 The female carries a conspicuous egg-sac on each side of the 

 abdomen, and reproduction occurs with such rapidity that 



oar ; Trews, foot. 



