. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 369 surface [Aphrodite). The appendages of the parapodia present an equally great variety of form and not unfrequently vary in the different parts of the body. They are either simple or ringed tenta- cle-like processes, the cirri, which are distinguishable into dorsal and ventral cirri. The cirri are for the most part filiform, and sometimes jointed or conical, and then are often provided with a special basal joint. In some cases the dorsal cirri are flattened out as broad scal
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 369 surface [Aphrodite). The appendages of the parapodia present an equally great variety of form and not unfrequently vary in the different parts of the body. They are either simple or ringed tenta- cle-like processes, the cirri, which are distinguishable into dorsal and ventral cirri. The cirri are for the most part filiform, and sometimes jointed or conical, and then are often provided with a special basal joint. In some cases the dorsal cirri are flattened out as broad scales and leaves, the elytra, which constitute a protective covering (Aphro- dite) (fig. 299). In addition to the cirri, branchiae which may be filiform or branched and antler-like, comb- shaped or in the form of tufts, are frequently present; sometimes they are confined to the middle region of the body, or are extended over almost the whole dorsal surface; sometimes they are confined to the head or to the anterior segments immediately following the oral segment (cephalic branchiae). The two anterior segments may be regarded as forming the head; they are fused together, and are, with regard to their appendages, different from the following segments (fig. 245). The anterior segment projects beyond the mouth as the frontal lobe, and bears the tentacles and palps [palps are ten- tacular structures arising from the ventro-lateral sides of the head, vide p. 379] and also the eyes ; the posterior cephalic segment or oral segment bears the tentacular cirri. The last segment (anal segment) bears the anal cirri. The alimentary canal is usually straight, and extends from the mouth to the anus, which is terminal and rarely dorsal; it is divided into oesophagus, intestine, and rectum (fig. 300). There is in most cases a dilated muscular pharyngeal bulb which is armed with papillae or with movable teeth and can be protruded as a proboscis. The intestine usually preserves the same structure in
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Keywords: ., book, bookcentury1800, bookcollectionbiodiversity, bookdecade1890
