BARNACLE, a degenerate crustacean of the order Cirripedia, living attached to some foreign object, such as wharf piles, rocks and the bottoms of ships. The barnacles would at first glance hardly be regarded as Crustacea at all, and were considered to be mollusca, until in 1836 Thompson found that the yotmg barna cle was like the larvm of other low Crustacea (Copepoda). The young barnacle is, as in the common sessile form, a shell-like animal; the shell composed of several pieces or valves with a multivalve, conical, movable lid, having an opening through which several pairs of long, many-jointed, hairy appendages are thrust, thus creating a current which sets in tovtard the mouth. The common barnacle balanoides) abounds on every rocky shore from extreme high-water mark to deep water, and the student can by putting a group of them in sea water, observe the opening and shutting of the valves and the movements of the ap pendages. The structure of the.barnacle may best be observed in dissecting a goose-barnacle (Lepas fascicularis). This barnacle consists of a body (capitulum) and leathery peduncle. There are, six pairs of jointed feet, represent ing the feet of the cyclops. The mouth, with the upper lip, mandibles, and two pairs of max Him, will be found in the middle of the shell. A short cesophagus leads to a pouch-like stomach and tubular intestine. This form, !lice most barnacles, is hermaphroditic, the ovary lying at the bottom of the shell, or, in the pedunculated forms, in the base of the pe duncle, while the male gland is either close to or some distance from the ovary. There is also at the base of the shell, or in the peduncle when developed,, a cement-gland, the secretion of which is for the purpose of attaching the barnacle, when in the "cyprisp stage, to sorne rock or weed.
While the sexes are generally united in the same individual, in the genera lbla arid Scalpel lum, besides the normal hermaphroditic form, there are females, and also males called (com plementary males,)) which are attached parasit ically both to the females and the hermaphro ditic forms, living just within the valves or fastened to the membranes of the body. These
complemental males are degraded, imperfect forms, with sometimes no mouth or digestive canal. The apparent design in nature of their &fferent sexual forms is to effect cross-fertili zation. The eggs pass from the ovaries into the body-cavity, where they are fertilized and remain for some time. They pass through a morula condition, a suppressed gastrula or two layered state, and hatch in a form called a "Nauplius,0 from the fact that the free-swim ming larva of the Entomostraca was at first thought to be an adult Crustacean, and de scribed under the name of Nauplius. The Nauplius of the genuine barnacles has three pairs of legs ending in long bristles, with a single eye and a pan. of antennm, the body end ing in front in two horns, and posteriorly in a long caudal spine. After swimming about for a while, the Nauplius attaches itself to some object by its antennce, and a strange transfor mation results. The body is enclosed by two sets of valves, appearing as if bivalved, like a cypris; the peduncle grows out, concealing the rudimentary antennw, and the feet become smaller, and eventually the barnacle shape is attained. The common barnacle (Balanus ba lanoides) attains its full size, after becoming fixed, in one season; that is, between April and November. Consult monographs on the Crus tacea by Charles Darwin (London 1851-54) ; 'Challenger Reports) (Vol. XXVIII); Hoek,
See PILE FISH.