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Show 332 MR. A. E. SHIPLEY ON THE GENUS SIPUNCULUS. [Apr. 18, (2)SELENKA, E.-Die Sipunculiden. Eine systematische Monographic Reisen im Archipel der Philippinen, Bd. iv. Abth. 1. (3) W A R D , H. B.-" On some Points in the Anatomy and Histology of Sipunculus nudus, L." Bulletin of the Museum of Comparative Zoology at Harvard College, vol. xxi. No. 3. (4) DANIELSSEN and KOREN.-Gephyrea. Den Norske Nordhaus- Expedition. Part iii. EXPLANATION OF THE PLATES. List a. Mouth. b. Anus. c. GGsophagus. d. Intestine. /. Nephridia. g. Retractor muscles. h. Brain. of Reference Letters. o. Sinuses in the same. p. Scales on the introvert. q. Papillae on scales. r. Rectum. s. Rectal tufts. t. Ducts of rectal tufts. u. Mesenteries supporting these ducts. i. Digitate process of Brain. v. Sinuses in wall of rectum. j. Ventral nerve-cord. k. Dorsal blood-vessel. /. Longitudinal muscles. m. Circular muscles. n. Tentacular fringe. w. Spindle muscle. x. Caecum dn intestine. y. Diverticula of dorsal vessel. z. Ciliated pit leading to brain. PLATE XXV. Fig. I. View of a Sipunculus indicus cut open by an incision a little to the right of the dorsal middle line. The introvert is extended and the viscera are exposed in situ. The drawing is f the natural size. 2. A portion of the same in the region of the oesophagus, magnified two diameters, to show the numerous bands of longitudinal muscles. 3. Two views, magnified, of the brain of Sipunculus tessellatus. The fig. to the right shows its position above the oesophagus and between the dorsal retractors. The fig. to the left is more highly magnified, to show the character of the digitate processes. PLATE XXVI. Fig. 4. A view of the head of S. indicus. The mouth is shown in the centre, and between it and the ring of tentacles run several vascular ridges. To the right are two sketches, more highly magnified, to show the characters of the scales on the introvert and the square areas in the trunk. 5. A dorsal view of the head of S. nudus with the tentacular fringe very much folded, X 4. The mouth is away from the spectator and the depression leading to the brain is near him. 6. A ventral view of another specimen of S. nudus, in which the fringe is not at all folded, the wall of the oesophagus is bulged forward and obliterated the oral orifice. 7. A n anterior view of the mouth of S. tessellatus. 8. A longitudinal section through the skin of the introvert of S. indicus, showing the structure of the scales, the prolongations of the body-cavity into them, and the ' papillae.' 9. A view of the rectum of S. tessellatus, showing the anal tufts, the enlargement of the alimentary canal to form the rectum, the spindle muscle, the muscular strands supporting the intestine, the caecum opening into the latter, and the longitudinal and circular muscles of the skin. |
