270 ENTOMOSTRACOUS CRUSTACEA. OSTRAPODA. 



of two or more joints. There is considerable resemblance, except 

 in the conformation of the mouth, between some of these and 

 the Suctorial Crustacea hereafter to be described, It is to this 

 group, that the term Entomostracous has been restricted by later 

 Naturalists ; but it is commonly applied to the minute Branchi- 

 opodous Crustacean just described, and even to the Limuli 

 ( 816), as well as to these all agreeing in the inclosure of the 

 body in a single or bivalve shell. 



808. In the Order OSTRAPODA, 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 antennas and feet to pass out between them. There 

 are two pairs of antennae ; of which the first (#, Fig. 495) 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. 495. CYPRIS upper and lower lip and a pair of mandibles, with 



VIDUA, magnified. . of which the poster ior 



carries a large flapper-like appendage, that is probably to be 

 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 Branchippus, 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 fema|e to water-plants, with the aid of a glutinous secre- 

 tion, an operation which lasts about twelve hours. There are 

 but two pairs of legs in this genus, of which the posterior does 

 not make its appearance outside the shell ; being bent upwards 



