. Outlines of zoology. Zoology. 268 CRUSTACEA. egg-cases, and, after moulting several times, become like little Cyprid water-fleas. The first pair of appendages become suctorial, and, after a period of free-swimming, the young barnacle settles down on some floating object, mooring itself by means of the antennary suckers, and becoming firmly glued by the secretion of the cement glands. During the settling and the associated metamorphosis, the young barnacle fasts, living on a store of fat previously accumulated. Many important changes occur, the valved shell is developed, and the adult form is
. Outlines of zoology. Zoology. 268 CRUSTACEA. egg-cases, and, after moulting several times, become like little Cyprid water-fleas. The first pair of appendages become suctorial, and, after a period of free-swimming, the young barnacle settles down on some floating object, mooring itself by means of the antennary suckers, and becoming firmly glued by the secretion of the cement glands. During the settling and the associated metamorphosis, the young barnacle fasts, living on a store of fat previously accumulated. Many important changes occur, the valved shell is developed, and the adult form is gradually assumed. While the early naturalists, such as Gerard (1597), regarded the barnacle as somehow connected with the barnacle-goose, and zoologists, before J. Vaughan Thompson's researches (1829), were satisfied with calling Cirripedes divergent Molluscs, we now know. Fig. 114. -Acorn-shell (Balanus tintinnabulum). —After Darwin. , Tergum ; j., scutum ; d., opening of oviduct, the aperture is not distinct',/., mantle cavity ; jr., depressor muscle of tergum ; g., depressor muscle of scutum; A., oviduct; outer shell in section; a., adductor muscle of scuta; cr., thoracic legs; 1, first plate of outer shell ; /., position of viscera. clearly that they are somewhat degenerate Ciustaceans. We do not know, however, by what constitutional vice, by what fatigue after the exertions of adolescence, 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 somewhat rapid, but the usual skin casting is much restricted, except in one genus. Neither the valves, nor the uniting membranes, nor the envelope of the stalk, are moulted, though disintegrated portions may be removed in flakes and renewed by fresh formations. In the allied genus Scalpellum, some are like Lepas, hermaphrodites, without complementary males (Sc. bala- noides); others are hermaphrodite, with complementary ma
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