CLADOCERA. 



2?9 



Fig. 235.— ActhereB of the trout 



The highest members of the group of sucking Entomo- 

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

 mented, with antennae and free 

 mouth-parts and legs ; the latter 

 genus with compound eyes. Cali- 

 gus curtus MUller lives on the cod, 

 and Argulus alosce Gould on the 

 alewife. 



Order 3. Branchiopoda. — This 

 order includes such Crustacea as 

 in the higher forms breathe by 

 rather broad feet. There is a 'con- 

 siderable range of 

 form from the 

 Ostracuda, repre- 

 sented by Gypris, 

 in which the feet 

 are much as in Cy- 

 clops, through Daplinia and Sida (Fig, 337) 

 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 antennae, 

 a pair of mandibles with a jointed feeler 

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

 the second pair often carrying a small gill. 

 The shells of certain species allied to Cypiris 

 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 youngest stage being a 

 shelled Nauplius. 



The suborder Cladocera is represented by 

 fresh and salt-water species. The higher 

 forms are Sida and Baplmia. They are 

 called water-fleas from their jerky motions. 

 The eggs of Daphnia are borne about by 

 Pig S30.-Peneiia of the females in so-called brood-cavities on 



the Bword-flsh, female. ^^^ -^^^^ ^^^^^ ^j^g g^^gjl_ rj^^vQVQ are tWO. 



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



