SECT. vn. CRUSTACEA. 209 



in pools and ditches, coming in groups to the surface 

 in the mornings and evenings in cloudy weather. The 

 bivalve shell is transparent, flexible, and open below ; 

 it ends behind in sharp toothed peaks. The eye placed 

 in front is moved by four muscles, and on each side of 

 it are the great antennae, which are jointed, branched, 

 and garnished with feathery filaments, and are the chief 

 organs of locomotion. This animal has no foot-jaws, 

 but it has a nervous system and a heart, whose pulsa- 

 tions are repeated two or three hundred times in a 

 minute, and the blood is aerated by gills at the extre- 

 mities of six pairs of bristly feet situated behind the 

 mouth, and only used for respiration and prehension. 



The eggs, when laid, are deposited in a receptacle 

 between the back and the shell of the female Daph- 

 nia, and after the young come into the water they 

 undergo no transformations. Between each brood the 

 Daphnia moults, and the egg receptacle is thrown off 

 with the exuvia. After several changes of skin the young 

 Daphnise come to maturity and lay eggs, which pro- 

 duce successive generations of females throughout the 

 spring and summer ; but in the autumn males appear, 

 and then the eggs are retained in the receptacle of the 

 female and are not hatched till spring. If the female 

 should moult after this, the case with the eggs in it is 

 cast off with her outer skin, which then becomes a pro- 

 tection to the eggs during the winter, and they are 

 hatched in spring, producing females. 



Phyllopoda. 



The second order of gill-footed Crustacea are called 

 Phyllopoda, because they have gills like the leaves of a 

 book attached to their lamelliform swimming feet. 

 Their bodies are divided into many segments, and they 

 form two groups, one of which has a carapace, the 



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