CLADOCERA. 279 



The highest members of the group of sucking Entomo- 

 straca are Caligus and Argulus, in which the body is seg- 

 mented, with antennae and free 

 mouth-parts and legs ; the latter 

 genus with compound eyes. Cali- 

 gus curtus Miiller lives on the cod, 

 and Argulus alosce Gould on the 

 alewife. 



Order 3. Branchiopoda. This 

 order includes such Crustacea as T 

 in the higher forms breathe by 1 

 rather broad feet. There is a con- 

 siderable range of 

 form from the 

 Ostracuda, repre- 

 sented by Cypris, 



in Which the feet Fi g . ^.-Actheres of the trout 



are much as in Cy- 

 clops, through Daphnia and Sida (Fig. 237) 

 which represent the Cladocera, up to the 

 Phyllopods. The suborder of Ostracoda 

 (Cypris) arebivalved, the shell often thick. 

 They have two eyes, two pairs of antennas, 

 a pair of mandibles with a jointed feeler 

 (palpus) and a gill, and four pairs of feet, 



/ "^l Ol second pair often carrying a small gill. 



\ J\ I ^e sne ^ s t cei 'tain species allied to Cypris 

 abound in the lowest Silurian strata. The 

 species live in fresh-water pools and in the 

 ocean at various depths. They undergo no 

 metamorphosis, the youl%est stage being a 

 shelled .Nauplius. 



The suborder Cladocera is represented by 

 fresh and salt-water species. The higher 

 forms are Sida and Daphnia. They are 

 called water-fleas from their jerky motions. 

 The eggs of Daphnia are borne about by 



Fig. 23c.-peneiia of the females in so-called brood-cavities on 

 the sword-fish, female. t i ie back under the s h e] ^ There are two 



sorts of eggs, i. e., the "summer" eggs, which are laid by 



