Ostracoda.
Our knowledge of the development of this remarkable group is entirely due to the investigations of Claus.
Some forms of Cythere are viviparous, and in the marine form Cypridina the embryo develops within the valves of the shell. Cypris attaches its eggs to water plants. The larvæ of Cypris are free, and their development is somewhat complicated. The whole development is completed in nine ecdyses, each of them accompanied by more or less important changes in the constitution of the larva.
Fig. 234. Two stages in the development of Cypris. (From Claus.)
A. Earliest (Nauplius) stage. B. Second stage.
A´. A´´. First and second pairs of antennæ; Md. mandibles; OL. labrum; Mx´. first pair of maxillæ; f´´. first pair of feet.
In the earliest free stage the larva has the characters of a true Nauplius with three pairs of appendages ([fig. 234] A). The Nauplius presents however one or two very marked secondary characters. In the first place it is completely enveloped in a fully formed bivalve shell, differing in unessential points from the shell of the adult. An adductor muscle (SM) for the shell is present. Again the second and third appendages, though locomotive in function are neither of them biramous, and the third one already contains a rudiment of the future mandibular blade, and terminates in an anteriorly directed hook-like bristle. The first pair of antennæ is moreover very similar to the second and is used in progression. Neither of the pairs of antennæ become much modified in the subsequent metamorphosis. The Nauplius has a single median eye, as in the adult Cypris, and a fully developed alimentary tract.
