Page:The aquarium - an unveiling of the wonders of the deep sea.djvu/245

194 that run out from the foot of Byng Cliff, I found in September a full grown specimen of the Velvet Fiddling Crab (Portunus puber). All the Crabs of this family, which contains a great number of species and not a few genera, are distinguished at once by a peculiar modification of the hindmost pair of feet, for the performance of an important function. They are all Swimming Crabs, and the facility with which they can roam through the element they inhabit, depends largely on the completeness of the modification which I refer to. Our common Eatable Crab, the bulky, thick-clawed, livid 8-pounder, that lies with all his ten pairs of feet so meekly folded across his breast, can swim—about as well as a stone of the same size. Now examine his hindmost feet; their single toe tapers to a sharp point in no wise differing from those of the four pairs that precede them. But the Portunidæ, or Swimming Crabs, have this last pair of feet much flattened out side-wise, and the toe in particular dilated into an oval thin-edged plate, which striking obliquely upon the water acts as an oar, with that peculiar action which is known to boatmen as sculling. In the common Shore-crab (Carcinus mænas), that abundant olive-green kind which on every rocky shore little boys and girls catch, by letting down into the crevices a piece of string with a fragment of offal tied to it,—we observe a transition condition of the hindfoot; there is a decided tendency to an ovate form, though the tip is yet taper and acute. And the habits of the animal agree with this structure. The power of shooting slantwise through the water exists, which bears the same sort of relation to the free and easy