Fig. 235. Stages in the development of Cypris. (From Claus.)
A. Fourth stage. B. Fifth stage.
Mx´. first maxilla; Mx´´. and f´. second maxilla; f´´. first pair of feet; L. liver.
The second stage ([fig. 234] B), inaugurated by the first moult, is mainly characterized by the appearance of two fresh pairs of appendages, viz. the first pair of maxillæ and the first pair of feet; the second pair of maxillæ not being developed till later. The first pair appear as leaf-like curved plates (Mx´) more or less like Phyllopod appendages (Claus) though at this stage without an exopodite. The first pair of feet (f´´) terminates in a curved claw and is used for adhering. The mandibles have by this stage fully developed blades, and have practically attained their adult form, consisting of a powerful toothed blade and a four-jointed palp.
During the third and fourth stages the first pair of maxillæ acquire their pectinated gill plate (epipodite) and four blades; and in the fourth stage ([fig. 235] A) the second pair of maxillæ (Mx´´) arises, as a pair of curved plates, similar to the first pair of maxillæ at their first appearance. The forked tail is indicated during the fourth stage by two bristles. During the fifth stage ([fig. 235] B) the number of joints of the first pair of antennæ becomes increased, and the posterior maxillæ develop a blade and become four-jointed ambulatory appendages terminating in a hook. The caudal fork becomes more distinct.
In the sixth stage ([fig. 236]) the second and hindermost pair of feet becomes formed (f´´´) and the maxillæ of the second pair lose their ambulatory function, and begin to be converted into definite masticatory appendages by the reduced jointing of their palp, and the increase of their cutting blades. By the seventh stage all the appendages have practically attained their permanent form; the second pair of maxillæ has acquired small branchial plates, and the two following feet have become jointed. In the eighth and ninth stages the generative organs attain their mature form.
Fig. 236. Sixth stage in the development of Cypris. (From Claus.)
Mx´. first maxilla; Mx´´. f´. second maxilla; f´´. and f´´´. first and second pair of feet; Fu. caudal fork; L. liver; S.D. shell-gland.
The larva of Cythere at the time of birth has rudiments of all the limbs, but the mandibular palp still functions as a limb, and the three feet (2nd pair of maxillæ and two following appendages) are very rudimentary.