THE DAPHNIA AND ITS ALLIES 



127 



ant.i 

 ant.Z 



abd.f 



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 1 

 is closely allied to the Clado- 

 cera. The common repre- 

 sentative of this family, 

 Branchipus, has an elongated, 

 distinctly segmented body 

 whicli carries eleven pairs 

 of lobed, leaf-like feet, func- 

 tioning both as respiratory 

 and locomotor organs. Like 



Daphnia, Branchipus pro- 



- FIG. 118.--Apus glacialis, ventral 



dlices Winter eggs Which Can aspect, abd.f., abdominal feet; 



Withstand desiccation even nt ' f > antennule ; ant. 2, antenna ; 



lor., labrum ; ma., mandible ; mx., 

 for years ; indeed, in Some 



cases, a certain amount of 

 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, 



1 j3pdyx ia -> gills ; Totfs, foot. 



2 HxrrpaKov, shell of a testacean ; eI5os, like. 



first maxilla; ov., aperture of ovi- 

 duct: .s. /. pi., sub-frontal plate; 

 s7f. f/l., shell-gland; tli.f., thoracic 

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

 After Bernard. 



