38 



THE LIFE OF CRUSTACEA 



where in ponds and lakes (Fig. 12). They are all 

 of small size, almost or quite microscopic. The 

 carapace, as in the Conchostraca, forms a bivalved 

 shell, but does not enclose the head. There is a 

 single large eye, which really corresponds to two 

 eyes fused together. A pair of large antennae, each 

 with two branches, carrying long feathered hairs, 

 project at the sides of the head, and are used in 



Fig. 13 — Shells of Ostracoda. Much enlarged. (From Lan- 

 kester's "Treatise on Zoology," after Brady and Norman, and 

 Miiller.) 



A, Philomedes hrenda (Myodocopa) ; B, Cypris fuscata (Podocopa) ; 

 C, Cythereis ornata (Podocopa). n, Notch characteristic of the 

 Myodocopa; e, the median eye; a, mark of attachment of the 

 muscle connecting the two valves of the shell. A and C are 

 marine species ; B is from fresh water 



swimming with a peculiar jumping motion, from 

 which the popular name of the animals is derived. 

 There are not more than six pairs of feet. The 

 " Water- fleas," of which Daphnia pulex is one of the 

 commonest species, are very beautiful and interesting 

 objects for microscopic examination, on account of 

 their transparency, which allows many details of their 

 internal structure to be studied in the living animal. 

 The Ostracoda (Fig. 13), which form the second 



