The sow-bugs or pill-bugs, common in gardens, under leaves in the woods, and under almost any pile of rubbish among decaying vegetable matter, are a land species of isopods. Other species inhabit [pg292] ponds and streams of fresh water, and still others are found along the shores of all oceans, abounding among the marine vegetation of the shallow waters. Some swim free in the open sea; others are brought up from the greatest depths. Others, again, are parasites, and live in the internal organs of fishes and prawns. Sometimes a prawn is found having what appears like a very swollen throat, which actually is a little parasitic isopod of the family /Bopyridæ/ attached to its gills. GENUS ^Cirolana^ [Illustration: /Cirolana concharum./] ^C. concharum.^ The body consists of fourteen segments, the first being the head, the next seven the thorax, and the last six the abdomen. On the head are the triangular eyes, the antennules, and the antennæ, and underneath is the mouth, which is covered by the maxillipeds. The dorsal surface is more or less rounded. At the bases of all the segmental thoracic rings excepting the first one are sutures marking off square, scale-like pieces (/epimera/). The epimera form a border to the side margins. The legs are attached to the epimera, which are, in fact, the upper segments of the legs. The first three pairs of legs have a general resemblance to one another, and are directed forward. The last four pairs are much longer and flatter, and are directed backward. The telson, or last segment, is triangular, and the square or blunt apex is fringed with hairs. On the ventral surface of the thorax in the adult females there is a long pouch for the reception and development of the eggs. This species is usually about one and a half inches in length, but sometimes is longer. Its color is yellowish, with a brown edge on the posterior margins of the segments, somewhat translucent in the thinner parts. It is found from Cape Cod to South Carolina, swimming about in shallow water, and is especially abundant in winter. GENUS ^Limnoria^ [Illustration: /Limnoria lignorum/, the gribble.]