CLADOCERA. 



279 



Fig. 235. Adheres of the trout 



The highest members of the group of sucking Entomo- 



sfcraca 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 



in the higher forms breathe by 



rather broad feet. There is a con- 

 siderable range of 

 form from the 

 Ostracoda, repre- 

 sented by Cypris, 

 in which the feet 

 are much as in Cy- 



clops, through Daplinia and Sida (Fig. 237) 

 which represent the Cladocera, up to the 

 Phyllopods. The suborder of Ostracoda 

 (Cypris) are bivalved, 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. 

 J\ | The shells of certain species allied to Cypris 

 =*r J*=Jl 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 Daplmia. They are 

 called water-fleas from their jerky motions. 

 The eggs of Daphnia are borne about by 

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



l> There a]>c tWQ 



which are laid by 



Fig 



the sword-fish, female. 



sorts of eggs, i. e., the 



" summer" eggs, 



