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Show 1903.] METAMORPHOSES OF DECAPOD CRUSTACEAXS. 25 no mention of these structures in the descriptions of any Crangon larva?, though they are certainly present both in C. trispinosus and in C. nanus. It seems to m e quite possible that they represent the frontal sensory processes which have been found on certain Cirripede nauplii for example, and which have been supposed to be the vestiges of a pair of preoral appendages. In the abdomen, the first and second segments are characterised by the lateral expansion of their epimera (PI. Y. fig. 1), which makes them appear considerably broader than the succeeding segments. The third segment bears dorsally two strong backward ly directed spines. In the fourth segment these spines are represented by a pair of very small knobs, while in the succeeding segment they are shifted somewhat laterally and have the form of a pair of long, downwardly curved, blunt processes. The tail-plate is of the usual Crangonid type, with seven strong ciliated spines on either side. These spines, however, are somewhat peculiar in having quite blunt terminations, a feature which persists in the later stages also. The first antenna? are unusually long-about two-thirds the length of the carapace. The inner flagellum, which is a direct prolongation of the stem, is ciliated and very bluntly pointed. This blunt termination looks at first sight like the result of an injury ; but as all the larva? were the same in this respect, this condition is clearly normal. The scale of the second antenna (PI. V. fig. 3) is long and very narrow, with seven internal seta?, two seta? and a short spine terminally, and two short external seta?. The first maxilla (PI. Y. fig. 4) has a two-jointed palp, and in other respects this appendage and the first maxilla also conform exactly to the characteristic crangonid type. The exopodite of the first maxillipede (PI. YI. fig. 6) has three apical seta?, and two seta? on its external edge, differing in this respect from Crangon vulgaris, which has but one external seta. In the endopodite I can detect only three joints, and in the same way in the other maxillipedes I can only make out four. Williamson shows the palp of the first maxillipede in Crangon vulgaris as distinctly divided into four joints, but though there are certainly four small lobes, I cannot trace the separation of the second segment into two, nor of the third segment in the case of the other two pairs. The more advanced larva? of Crangon fasciatus are comparatively rare in the tow-net collection, but four stages are to be distinguished in m y material. That corresponding to stage iv. of C. vulgaris, i. e. with the pleopocls represented by short buds, I have not found, though there can be but little doubt that it occurs. In the last stage (stage v.) the length of the body is about 3-5-3'8 mm., the rostrum extending about "2 m m . beyond the eyes. The form of the rostrum, which acquires its definitive shape in the second stage, differs from that of the first stage. |