Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 430 CRUSTACEA. (fig. 341), two toothed, usually palped mandibles are placed be- neath the upper lip. These function in the free-living Copepoda as masticatory organs, but in the parasitic forms are usually trans- formed into pointed styliform rods, which are used for piercing. In this case they are frequently placed in a suctorial tube formed by the junction of the upper and under lips. The two jaws which follow the mandibles are weaker biting plates, and in the parasitic Copvpoda are re
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 430 CRUSTACEA. (fig. 341), two toothed, usually palped mandibles are placed be- neath the upper lip. These function in the free-living Copepoda as masticatory organs, but in the parasitic forms are usually trans- formed into pointed styliform rods, which are used for piercing. In this case they are frequently placed in a suctorial tube formed by the junction of the upper and under lips. The two jaws which follow the mandibles are weaker biting plates, and in the parasitic Copvpoda are reduced to small palp-like protuberances. The maxil- lipeds, on the contrary, are much longer; they are used to procure food and, especially in the parasitic forms, to attach the body. The thoracic swimming feet consist of a two-jointed basal portion, and two three- jointed setigerous swimming raini, which are comparable to broad swimming plates. In the ArgulidfK these rami are much elongated, and by their numerous joints approximate to the legs of the Cirripedia. Nervous System.—In all cases there is a brain giving off sensory nerves, and also a ventral cord, which either develops some ganglia in its course or is concen- trated to a common subcesophageal gan- glionic mass. Of sense organs the median frontal eye, divided into three parts (Cy- clops eye), is pretty generally present. The tactile sense is specially localized in the sete of the anterior antenna?, but is probably also present in many other parts of the body. Olfactory hairs are pre- sent as delicate appendages of the an- terior antenna?, principally in the male sex. The alimentary canal is divided into a short narrow oesophagus, a wide sto- mach which often has two blind diverticula near its commence- ment, and a narrow rectum which opens on the dorsal surface of the last abdominal segment. The surface of the intestine often seems to perform the function of a urinary organ. We find, however, at the same time a shel
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