346 CLASS CRUSTACEA. 



animals appearing to be affected by this modification. On 

 the renewal of their testa, but slight traces of this alteration 

 are perceptible, and those are manifested by rugosities. 



These Crustacea cease to reproduce, and to moult, on the 

 approach of winter, and end by perishing before the com- 

 mencement of the frosts. The eggs contained in the ephippia, 

 which had been laid during the summer, disclose on the first 

 return of warm weather, the following spring. The pools are 

 then speedily repopulated with an infinite number of daphniae. 

 Many naturalists have attributed the sanguine colour which 

 these waters sometimes assume, to the presence of myriads 

 of the Daphnia Pulex. But M. Straus declares that he never 

 observed this fact, and that at all times this species is but 

 slightly coloured. In the morning and evening, and even 

 during the day, when the sky is cloudy, the daphnia; remain 

 habitually at the surface of the water. But during the very 

 warm weather, and when the sun shines strongly on the 

 pools or stagnant waters which they inhabit, they sink 

 into the water ; and remain at a depth of six or eight feet, or 

 more. Frequently, not a single one is to be seen at the sur- 

 face. They swim by little springs, of greater or less extent, 

 according as their oars are more or less long, and as the 

 buckler, which covers the front of their body, projects out- 

 wards, more or less, the largeness of this projection being 

 capable of impeding their movements. According to M. 

 Straus, their nourishment consists exclusively of small por- 

 tions of vegetable substances which these animals find at the 

 bottom of the water, and very often of confervas. They con- 

 stantly rejected the animal substances which he presented to 

 them. He has frequently seen them swallow their own ex- 

 crements, drawn in by the current of water produced by the 

 action of their feet, and which conveys their ordinary aliment 

 towards their mouth. The hooks which terminate the ex- 

 tremity ol" their tail, serve to cleanse their gills. 



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