. Elements of comparative zoology. Zoology. CRUSTACEA. 221. the ducts of the reproductive organs open to the exterior in the thoracic region, never in the abdomen. In almost all forms the eggs are carried about by the mother until they are hatched. In almost all the lower Crustacea the young escapes from the egg in a very immature condition, known as a Nauplius (fig. 49), a name given years ago under the be- lief that it was an adult. The nauplius has an unsegmented body, a single median eye, and only three pairs of appendages -antennulae, antennae, and mandibles—the antennulse being solely se
. Elements of comparative zoology. Zoology. CRUSTACEA. 221. the ducts of the reproductive organs open to the exterior in the thoracic region, never in the abdomen. In almost all forms the eggs are carried about by the mother until they are hatched. In almost all the lower Crustacea the young escapes from the egg in a very immature condition, known as a Nauplius (fig. 49), a name given years ago under the be- lief that it was an adult. The nauplius has an unsegmented body, a single median eye, and only three pairs of appendages -antennulae, antennae, and mandibles—the antennulse being solely sensory, while antennae and mandibles are used in both swimming and eating. In the higher Crustacea the nauplius stage is passed in the egg, and the young hatches in a more ad- vanced condition—sometimes closely like the adult in all except size. Growth is allowed for by frequent molts of the external cuticle of the body. Over 10,000 species of Crustacea are known, almost all of them aquatic, and the majority marine. Only a few, like the sow-bugs and land-crabs, live on the land. A few are vegetarians, some are parasites on other animals, but the majority are scavengers, feeding on decaying organic matter. The Crustacea may be conveniently divided into two subclasses: and Entomostraca. FIG. 49.—Nauplius stage of fairy- shrimp (Branchipus). After Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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