CLADOCERA. 
279 
The highest members of the group of sucking Entomo- 
straca are Caligus and Argulus, in which the body is seg- 
mented, with antenne and free 
mouth-parts and legs; the latter 
genus with compound eyes. Cali- 
gus curtus Miller lives on the cod, 
and Argulus alose 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, 
are much as in Cy- 
in which the feet Fig. 235,—Actheres of the trout. 
clops, through Daphnia 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 antenne, 
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 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 youngest 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 
236.—Penella of the females in so-called brood-cavities on 
Fig 
the sword-fsh, female, the back under the shell. 
There are two 
sorts of eggs, 7. ¢., the ‘‘summer” eggs, which are laid by 
