THE DAPHNIA AND ITS ALLIES 



127 



which forms its principal food. Another factor upon 

 which the number of Daphnia in a pond depends is tem- 

 perature. A high temperature seems to be unfavorable to 

 Daphnia, so that not the 

 summer, but the spring and 

 autumn are its periods of 

 maximum reproductive activ- 

 ity. This activity is like- 

 wise checked in winter even 

 though there is plenty of 

 food. 



The family Branchiopoda x 

 is closely allied to the Clado- 

 cera. The common repre- 

 sentative of this family, 

 Branchipus, has an elongated, 

 distinctly segmented body 

 which carries eleven pairs 

 of lobed, leaf -like feet, func- 

 tioning both as respiratory 

 and locomotor organs. Like 

 Daphnia, Branchipus pro- 

 duces winter eggs which can 

 withstand desiccation even 



FIG. 118. Apwt glacialis, ventral 

 aspect, abd. /., abdominal feet; 

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

 Ibr., labrum; md., mandible; mx., 

 for years; indeed, in SOme first maxilla; ov., aperture of ovi- 



cases, a certain amount of duct ; s /.^ sub-frontal plate ; 



sh. yl., shell-gland; th.f., thoracic 

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

 After Bernard. 



desiccation is a prerequisite 

 of hatching. Apus differs 

 from Branchipus in having a broad shield (Fig. 118). 

 The family Ostracoda 2 comprises some very abundant, 



*, foot. 

 , shell of a testacean ; e?5os, like. 



