. Animal physiology. Physiology, Comparative; Physiology, Comparative. 94 CIRRHIPODA, OR BARNACLE TRIBE. 113. In this portion of the Articulated series we must place a small but very remarkable group of animals, which were for some time associated with the Mollusca; their bodies being enclosed in shells, which do not fit closely around them, nor give more than a general protection to their members. This group is the Barnacle tribe, forming the class Cirrhipoda, or tendril- footed animals. They agree with the lower Mollusca, in being fixed to one spot during all but the earliest period of their
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 94 CIRRHIPODA, OR BARNACLE TRIBE. 113. In this portion of the Articulated series we must place a small but very remarkable group of animals, which were for some time associated with the Mollusca; their bodies being enclosed in shells, which do not fit closely around them, nor give more than a general protection to their members. This group is the Barnacle tribe, forming the class Cirrhipoda, or tendril- footed animals. They agree with the lower Mollusca, in being fixed to one spot during all but the earliest period of their lives; the shell being sometimes attached by a long membranous or leathery tube, as that of the Barnacle (Fig. 54) ; and sometimes being itself fixed on the surface of a rock, or on another shell, as is that of the Balanus or acorn-shell. In both cases, the form and structure of the animal are essentially the same. When taken from the shell (in which it lies doubled up, as it were,) and spread out, its articulated nature is evident, by its division into segments, and by the regula- rity of the arrangement of their tendril-like appendages. Fig. 55—Body of These are not formed like the barnacle. \eg$^ since they could be made no use of, the animal being incapable of moving from place to place ; but they serve to produce currents in the surrounding water, by which food is brought to the mouth, and the blood is submitted to the influence of a fresh supply of air. (§. 298.) The nervous system of this class is formed precisely upon the plan of that of the Articulated in general (§. 71) : and if any doubt could have remained as to its true place in the series, it is re- moved by the knowledge of the fact, that the animals composing it bear a strong resemblance, in their early condition, to some of the lower Crustacea, possessing eyes and legs, and swim- ming freely about; and that they attain their adult form by passing through a series of metamorphoses, in which they. Please not
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