. Animal biology. Zoology; Biology. A B Fig. 163.—Barnacles. A, Bdlanus hameri Darwin. The shell of the animal is closed up, concealing the occupant. B, Balanus tintinnabuium Linnaeus, showing the internal anatomy of the animal, also with the shell closed. (From Bronn, "Klassen und Ordnungen des Tierreichs," after Charles Darwin.) Natural size. ticularly entomostracans. These are exceedingly active, swimming or darting here and there and seeking that light intensity to which they are best adapted. Owing to the fact that some are adjusted to bright light and others to dim, there is a
. Animal biology. Zoology; Biology. A B Fig. 163.—Barnacles. A, Bdlanus hameri Darwin. The shell of the animal is closed up, concealing the occupant. B, Balanus tintinnabuium Linnaeus, showing the internal anatomy of the animal, also with the shell closed. (From Bronn, "Klassen und Ordnungen des Tierreichs," after Charles Darwin.) Natural size. ticularly entomostracans. These are exceedingly active, swimming or darting here and there and seeking that light intensity to which they are best adapted. Owing to the fact that some are adjusted to bright light and others to dim, there is a vertical migration in bodies of water of considerable depth which brings to the surface in the daytime certain forms which migrate to deeper levels at night. Others which remain at these deeper levels in the daytime come to the surface at night. In addition to light stimuli, crustaceans respond to contact and to chemical stimulation. 302. Reproduction.—Most crustaceans are diecious, though the barnacles are not. The eggs are centrolecithal, undergo superficial cleavage, and from them are produced larvae, which, as in the crayfish, may be miniatures of the adults, or which, as in the shrimp, may be quite different and pass through several larval stages, thus undergoing complicated metamorphoses. The young of crabs have very prominent eyes and for this reason have received the name of megalops. Many crustaceans carry their eggs about attached to abdominal appendages and in some cases contained in a brood pouch. The larvae may also be so carried for a 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 Wolcott, Robert Henry, 1868-1934. New York ; London : McGraw-Hill Book Company, Inc.
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