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Show 1903.] ANATOMY OF A NEW GEPHYREAN WORM. 33 series of papillae whose epithelial covering is apparently devoid of cilia. For the reason mentioned at the beginning of this paper, it was no easy matter to gain a certain knowledge of the histology of the alimentary tract. Figure 9 A (Plate V II.) shows the character of the epithelium of the mid-gut generally : lying upon the thin muscular wall are narrow cells of varying length, with a basal nucleus and granular cytoplasm; the outlines between the several cells were in many places most indistinct. The epithelium of the rectum (fig. 9 B) is composed of cubical cells, with a distinct margin on the surface next the lumen of the gut. They possess cilia, and were the only cells in the alimentary tract in which the presence of a ciliated border could with certainty be determined. Circulatory System. This consists of a dorsal vessel, a sinus surrounding the base of the tentacles, and tentacular vessels. The dorsal vessel is single, and though convoluted it is devoid of diverticula: coursing along the dorsal wall of the fore gut, it surrounds the base of the tentacles with a circular sinus into which the brain dips (Plate V III. figs. 11, 15, 16); from this circular vessel tentacular sinuses arise, they form noticeable objects in sections of the tentacles (Plate V II. fig. 8, B.S.). Are?'vous System. This is of the usual type, and consists of a brain, a ventral nerve-chain, and a couple of sense-organs. The brain is a small, somewhat cordiform body, measuring in its long axis, which corresponds with that of the animal, three-tenths of a millimetre; it lies on the dorsal wall of the pharynx at the base of the tentacles; it is surrounded by a fine capsule of con-nective- tissue, and the anterior surface in addition is covered by an epithelium (Plate V III. fig. 13, E.), which is continuous with that of the outer non-ciliated aspect of the tentacles; laterally, the muscular tube formed by the union of the retractors abuts upon it (fig. 15, R .M .); below the brain is the blood-sinus (B.S., figs. 11, 13, 15) from which the tentacular vessels arise. The majority of the cerebral cells are small, with a clear cytoplasm and relatively large nuclei; they are massed anteriorly, dorsally, and posteriorly: the central and greater part of the ventral aspect of the brain are composed of fibres, but behind the point of origin of the circumcesophageal commissures there are to be seen in the lower cortical part several very large ganglion-cells (G.C., fig. 11): these giant cells measure '03 mm. in diameter; some are pyriform, others irregular in shape, and these appear to be multipolar, unlike those of Phymosoma (Shipley, No. 7 l), but on this point I cannot be absolutely definite. 1 This number has reference to the list of authors quoted on p. 40. P r o c . Z o o l . S o c .- 1903, V o l . I. No. III. 3 |
