292 Miscellaneous. 



and he now completes this subject by describing all the phases of 

 the development of two other species of that genns. 



In contrast to the Cytherides, which present an advanced stage of 

 development at their first appearance, the young freshwater Ostra- 

 coda on quitting the egg only possess the three anterior pairs of 

 limbs, like the Nauplius of the Copepoda and Cirripedia. They are 

 distinguished, indeed, from these by the presence of a bivalve shell, 

 which protects them, and by the form of the limbs, of which the 

 first two pairs at least already present the general forms of the cor- 

 responding members in the adults. Nevertheless, from a morpho- 

 logical point of view, we may justly regard the young Cyprkles as 

 Nauplii, especially as the third pair of members in these little crea- 

 tures displays, both in form and function, peculiarities belonging to 

 that larval form. As in other Nauplii, in fact, the third pair of 

 limbs, corresponding to what will afterwards be the mandibles, do 

 not fulfil the function of jaws, but that of locomotive organs. They 

 arc triarticulate reptatory feet, the extremity of which terminates in 

 a strong bristle curved into a hook. In the older larvao of the Co- 

 pepoda the mandible buds as a masticatory process at the base of 

 this limb ; and so also the reptatory foot of the larvse of Gijpris pre- 

 sents at its base a crenulated apophysis, which, at the first change 

 of skin, bcomes converted into a mandible. 



The larvae of Cypris pass through a great number of stages before 

 arriving at their ultimate form and at sexual maturity. M. Claus 

 enumerates nine of these phases, separated from each other by a 

 complete moult and by a change of the shell. The most striking 

 character of the second phase is the budding forth of the mandibles 

 above mentioned, accompanied by the metamorphosis of the loco- 

 motory foot of the preceding phase into a mandibular palpus. At 

 this same period appear the rudiments of the maxilloj and of the 

 first pair of final locomotory feet. The jaw-feet (maxillae of the 

 second pair) appear in the fourth phase, and consequently after the 

 first pair of feet, which, however, come after them in the order of 

 succession of the appendages. During the fifth phase, the jaw-feet 

 plaj' the part of locomotory feet, and terminate in a strong hooked 

 bristle. In all phases of development there exists a pair of strong 

 posterior terminal bristles. It is singular that the position and inser- 

 tion of this bristle is modified in the course of development. Originally 

 it is borne by the mandibular foot, then by the first foot-rudiment, then 

 by the jaw-foot, and then by the locomotory foot of the first pair. 

 The posterior pair of locomotory feet appear at the sixth phase. At 

 the seventh all the extremities have nearly acquired their definitive 

 form. This is the period at which the first rudiments of the gene- 

 rative organs make their appearance ; but the sexual differences are 

 not manifested until the eighth stage. The abdomen or postabdo- 

 mcn appears in the fifth phase, in a form exactly similar to that of 

 the rudiments of the limb. This is also the period when the hepatic 

 canals grow and descend into the shell. — Scliriftcn der Geselheli. zur 

 Bcford. der (jes. Nahirw. in Marlnmi, V>(\. ix. ]8()S, p. lol ; Bihl. 

 Univ. tome x'xxv. August 15, lS()i), jinll. Sei. pp. 311^-814. 



