DAPilNlA : A STUDY OF THE FOOlJ OF Fl.SllES 1.37 



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One genus (Arteinia) loves water that is even denser than sea- 

 water. It lives in the Great Salt Lake and in vats where salt 

 is crystallizing out. To the genus Apus (Fig. 154) belongs the 

 largest of our fairy shrimps, 

 which is conspicuous because of 

 its broad shell. 



The water-fleas or Gladoc'era 

 include Daphnia and numerous 

 other very short Eiitomostraca 

 that are much flattened from 

 side to side (Fig. 155). They 

 live in ponds and lakes all over 

 the glol^e. During the autumn 

 in northern latitudes certain 

 species lay fertilized eggs that 

 may lie dormant for a year or 

 more. During the greater part 

 of the year females alone occur, 

 and unfertilized eggs (called also 

 " parthenogenetic " or " sum- 

 mer " eggs) are alone produced. 



The body of Daphnia is en- 

 closed in a heavy shell. This 

 makes the Daphnia so heavy 

 that it tends to sink in the water 

 and is only kept up by the vig- 

 orous swimming strokes of the 

 legs and its great antenna; or feelers which increase the friction 

 with the water, so that falling is less rapid. 



The family of bivalve entomostraca or Os'tracoda ^ comprise 



^ ostrakon, shell of a testacean ; eidos, like. 



Fig. 1.54. — Apus ylacialis, ventral 

 a.spect. abd.f, abdominal feet ; 

 arU. 1, antennule ; ant. 2, antenna ; 

 //(/■, labrum ; md, mandible ; -mx, 

 first maxilla ; ov, aperture of ovi- 

 duet ; sj.pl, sub-frontal plate ; 

 sh.gl, shell-gland ; Ih.f, thoracic 

 feet : th.f. 1, first thoracic foot. 

 After Bernard. 



