. Outlines of zoology. Zoology. 274 CRUSTACEA. and zoologists, before J. Vaughan Thompson's researches (1829), were satisfied with calling Cirripedes divergent Molluscs, we now know clearly that they are somewhat degene- rate Crustaceans. We do not know, however, by what con- stitutional vice, by what fatigue after the exertions of adoles- cence, they are forced to settle down to sedentary life. The food consists of small animals, which are swept to the mouth by the waving of the curled legs. Growth is some- what rapid, but the usual skin casting is much restricted ex- cept in one genus. Neith
. Outlines of zoology. Zoology. 274 CRUSTACEA. and zoologists, before J. Vaughan Thompson's researches (1829), were satisfied with calling Cirripedes divergent Molluscs, we now know clearly that they are somewhat degene- rate Crustaceans. We do not know, however, by what con- stitutional vice, by what fatigue after the exertions of adoles- cence, they are forced to settle down to sedentary life. The food consists of small animals, which are swept to the mouth by the waving of the curled legs. Growth is some- what rapid, but the usual skin casting is much restricted ex- cept in one genus. Neither the valves, nor the uniting mem- branes, nor the envelope of the stalk, are moulted, though dis- integrated portions may be re- moved in flakes and renewed by fresh formations. In the allied genus ScalpeUiun, some are like Lepas, hermaphrodites, without complementary males (Sc. balanoides) ; others are hermaphrodite, with comple- mentary males {Sc. villosuiit), &c. ; and others are unisexual, but the males are minute and parasitic (Sc. regiunt). Balanus^ the acorn shell, en- crusts the rocks in great num- bers between high and low water marks. It may be de- scribed, in Huxley's graphic words, as a crustacean fixed by its head, and kicking the food into its mouth with its legs. The body is surrounded, as in Lepas, hy a fold of skin, which forms a rampart of six or more calcareous plates, and a four- fold lid, consisting of two scu/a and two ferga. When covered by the tide, the animal pro- trudes and retracts between the valves of the shell six pairs of curl-like thoracic legs. The structure of the acorn shell is in the main like that of the barnacle, but there is no Fig. 90.—Development of Sacculina. (After \ge.) (Not drawn to scale.) A. Free swimming Nauplius, with three pairs of .-ippendages ; H. Pupa stage ; C. Adult protruding from the tail of a Please note that these images are extracted from scanned page images that may have been digitally enh
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
