. Animal biology. Zoology; Biology. 336 METAZOAN PHYLA life, since they commonly enter the gills or mouths of dead fishes and remain in the body, feeding upon it, until they have completely destroyed all but the skin and skeleton. They also may attack living fish, if these are disabled. Marked characteristics are the possession of four pairs of tentacles around the mouth, the presence of but one semicircular canal in the inner ear, a large number of gill slits, and a functional pro- nephros in the adult. There is no metamorphosis in the hagfishes. 359. Lampreys.—The mouth of the lampreys (Fig.
. Animal biology. Zoology; Biology. 336 METAZOAN PHYLA life, since they commonly enter the gills or mouths of dead fishes and remain in the body, feeding upon it, until they have completely destroyed all but the skin and skeleton. They also may attack living fish, if these are disabled. Marked characteristics are the possession of four pairs of tentacles around the mouth, the presence of but one semicircular canal in the inner ear, a large number of gill slits, and a functional pro- nephros in the adult. There is no metamorphosis in the hagfishes. 359. Lampreys.—The mouth of the lampreys (Fig. 224J5) is provided with an oral funnel armed with chitinous teeth (Fig. 225). Cartilages are present in the skull, about the notochord, around the gills, and in connection with the fins, but the notochord remains in full development. The number of gill slits is usually seven. The functional kidney in the adult is a mesonephros. The ureter opens into a urinogenital sinus, which also receives the sex cells liberated in the body cavity from the Notochord Dorsal aorfia Ncfsal opening Olfactory sac Dorsal cartilages y_4nnulcir cartilage. Buccal cat^ity with chitinous teeth Mouth Internal openings of Esophagus gill slits Tongue cartilage Annu/ar cartilage Fig. 225.—Median longitudinal section of the anterior part of the body of an adult sea lamprey. From a specimen. X '4- gonad. The brain is primitive, in many respects resembles that of the embryos of higher forms, and has a very small cerebellum (Fig. 226). The spinal cord is much flattened dorsoventrally. There are two semi- circular canals in the ear. Lampreys live in both fresh and salt water and are active and pre- daceous, attacking fish much larger than themselves. They attach themselves to their prey by means of the sucker-like oral funnel, which is prevented from slipping by the chitinous teeth it contains. The flesh of the fish is then lacerated with the sharp chitinous end of the tongue so that blood and lymph can be
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