266 H. Rathke on the Metamorphosis of the Crustacea. 



considerable changes, so that these specimens now exhibited 

 great similarity with full-grown specimens. The legs, with 

 respect to form, were perfectly developed: indeed the six 

 front ones had already attained such a size that they exceeded 

 the cephalothorax in length. Also that portion of the cephalo- 

 thorax to which the legs were attached, had acquired, in re- 

 spect to length, the ascendency over that with which the 

 foot-jaws and cibarian apparatus are connected. The foot- 

 jaws were very much compressed, and possessed but a slight 

 magnitude in comparison to the legs ; they were, however, 

 with respect to form, already similar to those of the full- 

 grown specimens. Those of the front pair, which previously 

 were the largest, appeared at present the smallest; and in- 

 deed they had lost in circumference, their two branches had 

 shortened perceptibly, and on the inner ramification even the 

 articulation was missing, while the stem was further developed. 

 The outer branch (the palpus) on the central and posterior 

 foot-jaws was the longest, consisting of three articulations, 

 and had therefore acquired a joint more (the newly added joint, 

 which was now the terminal one, subsequently separates into 

 several.). The inner branch had become shorter on the central 

 foot-jaws, longer on the contrary on the posterior ones, so 

 that it now appeared altogether greater on the latter. Bran- 

 chiae were already present on the legs and posterior foot-jaws. 

 The antennae were of the same form as in full-grown spe- 

 cimens, yet the long flagellum of the posterior or outer 

 antennae only consisted of fifteen articulations. The eyes 

 also were already formed as in mature specimens, and directed 

 anteriorly. The snout had entirely disappeared. The tail, 

 it is true, had become broader, but not thicker in the same 

 degree, and appeared therefore rather flattened; its joints 

 were still more sharply separated from each other ; no lateral 

 curvature was yet perceptible on it. The central lamina of 

 the fan appeared like an oval cut from off* the thinner extre- 

 mity, and held together with the sixth joint of the tail by this 

 truncated end ; it had therefore quite a different form from 

 that in the less developed young. The lateral plates of the fan 

 had likewise, it is true, a resemblance to those of full-grown 

 individuals, but were still quite flat and thin; moreover, those 

 of the right and left half were still equal to each other in 

 size. 



3. Galathaea rugosa. — Mature embryos of this crab have a 

 structure and form similar to those of Pagurus. They like- 

 wise, therefore, have only three pair of locomotive organs, and 

 in all probability these are subsequently developed into foot- 

 jaws. They only differ from those of Pagurus, in the two 



