272 ENTOMOSTRACOUS CRUSTACEA. OSTRACODA. 



ORDER IX. OSTRACODA. 



882. We are now arrived at a group of Masticatory Crusta- 

 ceans, in which we lose all trace of organs peculiarly adapted for 

 respiration, the feet not being modified for this purpose, as in 

 the last Section, but being expressly formed for swimming, each 

 member being terminated by two oars composed of two or more 

 joints. There is considerable resemblance, except in the conform- 

 ation of the mouth, between some of these and the Suctorial 

 Crustacea hereafter to be described. 



883. In the Order OSTRACODA, the body does not exhibit a 

 division into distinct rings, and is altogether inclosed between 

 the two valves of a bivalve shell. This shell is furnished with 

 a hinge, like that of a bivalve Mollusk ; and can be closed in 

 such a manner as to envelop the animal completely; but the 

 valves are in general sufficiently wide apart, to allow the extremi- 

 ties of the antennse and feet to pass out between them. There 

 are two pairs of antennae ; of which the first (a, Fig. 605) is 



slender, whilst the second (b) is large, directed 

 downwards, and adapted for swimming. The 

 mouth is situated near the middle of the inferior 

 surface of the body ; it is furnished, besides an 

 FIG. 605.-CYPRIS upper and lower lip and a pair of mandibles, with 

 VIDUA, magnified. twQ paif Q mBX flfa . O f wn i c h the posterior carries 



a large flapper-like appendage, which is regarded as a branchial 

 organ. The true thoracic feet are only four or six in number. 

 The body terminates in a bifid tail ; and the eggs are lodged, as 

 in the Daphniae (to which these animals bear a strong general 

 resemblance), in a cavity between the back and the shell. The 

 principal genus of this Order is the Cypris, which, like the 

 Daphnia and the Chirocephalus, is an inhabitant of pools and 

 streams ; and strongly resembles the former of these, in regard 

 to its moultings and the deposition of its eggs. The young are 

 not born alive, however ; for the mass of eggs, including about 

 twenty-four, is attached by the female to water-plants, with the 



