The second maxillipede (fig. 45, B) has essentially the same composition as the first, but the exopodite (_ex_) is relatively larger, the endopodite (_ip–dp_) smaller and softer; and, while the ischiopodite (_ip_) is the longest joint in the third maxillipede, it is the meropodite (_mp_) which is longest in the second. In the first maxillipede (fig. 45, A) a great modification has taken place. The coxopodite (_cxp_) and the basipodite (_bp_) are broad thin plates with setose cutting edges, while the endopodite (_en_) is short and only two-jointed, and the undivided portion of the exopodite (_ex_) is very long. The place of {167} the podobranchia is taken by a broad soft membranous plate entirely devoid of branchial filaments (_ep_). Thus, in the series of the thoracic limbs, on passing forwards from the third maxillipede, we find that though the plan of the appendages remains the same; (1) the protopodite increases in relative size; (2) the endopodite diminishes; (3) the exopodite increases; (4) the podobranchia finally takes the form of a broad membranous plate and loses its branchial filaments. Writers on descriptive Zoology usually refer to the parts of the maxillipedes under different names from those which are employed here. The protopodite and the endopodite taken together are commonly called the _stem_ of the maxillipede, while the exopodite is the _palp_, and the metamorphosed podobranchia, the real nature of which is not recognised, is termed the _flagellum_. When the comparison of the maxillipedes with the abdominal members, however, had shown the fundamental uniformity of composition of the two, it became desirable to invent a nomenclature of the homologous parts which should be capable of a general application. The names of protopodite, endopodite, exopodite, which I have adopted as the equivalents of the “stem” and the “palp,” were proposed by Milne-Edwards, who at the same time suggested _epipodite_ for the “flagellum.” And the lamellar process of the first maxillipede is now very generally termed an epipodite; while the podobranchiæ, which have exactly the same relations to the following {168} limbs, are spoken of as if they were totally different structures, under the name of branchiæ or gills. The flagellum or epipodite of the first maxillipede, however, is nothing but the slightly modified stem of a podobranchia, which has lost its branchial filaments; but the term “epipodite” may be conveniently used for podobranchiæ thus modified. Unfortunately, the same term is applied to certain lamelliform portions of the branchiæ of other crustacea, which answer to the laminæ of the crayfishes’ branchiæ; and this ambiguity must be borne in mind, though it is of no great moment.