. The anatomy of the common squid, Loligo pealii, Lesueur. Squids; Mollusks. 33 of chitin are supported by a tough sheet of connective tissue, known as the subradular membrane. At the ventral end of the radular sac the tooth bearing portion of this membrane is reflected downward over the lower surface of the odontophore between it and the tongue, while the toothless portion of the mem- brane is reflected backward over the sides and top of the odontophore. The teeth (Text figure 12) are arranged in seven longitudinal and an indefinite number of transverse rows. Each transverse row consists of a
. The anatomy of the common squid, Loligo pealii, Lesueur. Squids; Mollusks. 33 of chitin are supported by a tough sheet of connective tissue, known as the subradular membrane. At the ventral end of the radular sac the tooth bearing portion of this membrane is reflected downward over the lower surface of the odontophore between it and the tongue, while the toothless portion of the mem- brane is reflected backward over the sides and top of the odontophore. The teeth (Text figure 12) are arranged in seven longitudinal and an indefinite number of transverse rows. Each transverse row consists of a central tooth flanked by three pairs of lateral teeth and has, at each end, a flat oval plate of chitin. The central tooth has a strong middle point and a pair of lesser lateral points. The tooth at either side of the center consists of a large inner and a smaller outer point. The teeth of the second and third rows from the center are strong, long, curved spikes. New teeth are constantly produced at the base of the radula and gradually push outward until they reach the mouth of the sac where they are drawn downward and then back- ward over the end Of the odonto- phore. While in the radular sac, the points of the teeth project toward its base (backward) but as they are drawn over the end of the odonto- phore the teeth point first upward and then forward so that they rasp food only as the radula is drawn into its sac. Two pairs of muscles, the radular retractors and protractors, draw the radula in and out over the apposed ends of the two radular cartilages which support it. These cartilages lie at the side of the radular sac and are slightly curved upward at each end. The dorsal ends of the rod-shaped cartilages are fastened to the lower part of the dorsal end of the upper jaw by means of muscle fibres which radiate backward, inward and forward from the jaw to the cartilage. The upper, i. e. the concave, side of each cartilage is covered, except at the end, by a trans- verse mus
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmollusks, bookyear191
