Elementary zoology (1902) Elementary zoology elementaryzoolog00kell Year: 1902 420 ELEMENTARY ZOOLOGY young barnacle just from the egg is a six-legged, free- swimming larva (nauplius) with a single eye, greatly like a young prawn or crab. It develops during its independ- ent life two compound eyes and two large antennae. But soon it attaches itself to some stone or shell, or pile or ship's bottom, giving up its power of locomotion, and its further de- velopment is a degeneration. It loses its compound eyes and an- tennae, and acquires a protecting shell. Its swimming feet become modified into
Elementary zoology (1902) Elementary zoology elementaryzoolog00kell Year: 1902 420 ELEMENTARY ZOOLOGY young barnacle just from the egg is a six-legged, free- swimming larva (nauplius) with a single eye, greatly like a young prawn or crab. It develops during its independ- ent life two compound eyes and two large antennae. But soon it attaches itself to some stone or shell, or pile or ship's bottom, giving up its power of locomotion, and its further de- velopment is a degeneration. It loses its compound eyes and an- tennae, and acquires a protecting shell. Its swimming feet become modified into grasping organs, and it loses most of its outward resemblance to the typical mem- bers of its class. The Tunicata or ascidians compose a whole group of animals which are fixed in their adult condition and have thus become degenerate. They have been likened to a 'mere rooted bag with a double neck.' In their young stage they are free-swimming, active, tadpole- like or fish-like larvae, possessing organs much like those of the adult simplest fish or fish-like animals. Their larval structure reveals, however, the relationships of the ascidians to the vertebrates, a rela- tionship which is not at all apparent in the degenerate adults. Certain insects live sedentary or fixed lives. All the members of one large family, the Coccidae, or scale- insects (figs. 62 and 63), have females which as adults are wingless and in some cases have no legs, eyes, or antennae, while the males are all winged and have legs and the Fig. 160.—Larva of a sphinx- moth, with cocoons of a para- sitic ichneumon fly. (From specimen.)
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