An indication of the way in which the degenerate Rhizocephala have been derived from normal Cirripedes is given by a peculiar species of pedunculate Barnacle, _Anelasma squalicola_, which lives attached to Sharks and Dogfish in the North Sea. In _Anelasma_ the peduncle becomes deeply buried in the flesh of the Shark, and its surface is covered with short branching, root-like filaments. As in the case of the Rhizocephala, these roots appear to absorb nutriment from the host, and, although _Anelasma_ possesses a food-canal and mouth, the cirri are reduced in size and devoid of hairs, so that they cannot be used for obtaining food as in ordinary Barnacles. CHAPTER XI CRUSTACEA IN RELATION TO MAN The Crustacea come into relation with human life in the most obvious and direct way in the case of those species that are used for food. The number of species so used in various parts of the world is very large, almost the only necessary condition being that the species shall be sufficiently large and abundant to make it worth while to fish for it. As most of the larger Crustacea belong to the Decapoda, it is this order that supplies practically all the edible species, almost the only exceptions being a few Barnacles which are eaten in various parts of the world. Thus the sessile Barnacle _Balanus psittacus_, found on the coasts of Chili, and growing to a length of 9 inches by 2 or 3 inches diameter, is, according to statements quoted by Darwin, "universally esteemed as a delicious article of food," and the pedunculate _Pollicipes cornucopia_ is used for food on the coasts of Brittany and Spain. By far the most valuable of all the edible Crustacea are the European and American Lobsters (_Homarus gammarus_ and _H. americanus_). The former is found on the coasts of Europe from Norway to the Mediterranean, living mostly a short distance below low-water mark wherever the bottom is rocky. At some places, as for instance at Worthing, Lobsters are common on a sandy bottom, but as a rule they seem to prefer localities where the crevices of a rough hard bottom afford abundance of shelter. They are usually caught in traps known as "Lobster pots" or "creels," which vary in construction in different localities. In some cases they are made of wicker-work, hemispherical in shape, with a funnel-shaped opening on top, so devised as to permit the Lobsters to enter easily, while preventing their escape. Another form is semi-cylindrical, with a framework of wood covered with netting or with wooden spars, and having two funnel-shaped entrances at the sides. These traps are baited with pieces of fish, preferably stale, and are sunk in suitable places, each attached by a line to a buoy or float.