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Show 1893.] MR. A. E. SHIPLEY ON THE GENUS SIPUNCULUS. 329 are to be found. Each scale is covered externally by a thin layer of cuticle, and on the upper exposed surface of the scale is a thin granular layer, outside the cuticle. This also shows faint and very fine striations. The papillae all open upon this surface and never upon the under surface, and it has occurred to m e that this outermost layer, confined to the same region of the surface, may be formed by the excretion of the granular cells of the papillae. Plate X X V . fig. 1 represents the appearance of one of the four specimens of S. indicus laid open by an incision a little to the right of the median line. The alimentary canal is very slender ; the mouth and oesophagus are lined by cilia; the anus is situated about the level of the junction of the anterior fifth with the posterior four-fifths of the total body length when fully extended. The descending loop of the intestine is much thicker than the ascending, anteriorly it is prolonged into several short loops. The coils of the two limbs of the intestine are very loose, and I did not detect any spindle muscle; the whole alimentary canal is, however, supported by numerous muscular strands given off from the longitudinal muscles. There are two brown tubes, which open to the exterior near the posterior end of the introvert. Their internal ciliated frilled opening is at the same level. The diameter of the nephridia is very uniform, and each is attached closely to the body-wall throughout its length by a number of muscle-strands, so that the great inequaHtv of size and position which is frequently noticed in these organs in other species is scarcely possible in Sipunculus indicus. Tbe heart does not extend very far down the oesophagus. It was difficult to make out its exact limit, as this part of the body was embedded in a caked coagulum of the coelomic fluid. I did not succeed in finding any of the branched diverticula of the dorsal vessel which are not uncommon in other unarmed Gephyrea. These diverticula are well shown in Sipunculus cumanensis, and a section through the oesophagus of this form is drawn in Plate XXVII. fig. 11. There are four retractor muscles which arise from about t\ie same level, almost halfway between the mouth and the anus. The ventral nerve cord is conspicuous; it gives off very numerous paired nerves which pass into the skin. At the posterior end of the body it is swollen into a small lump. I was not able to detect any traces of generative ridges. The Projections in the Brain. The curious finger-like projections on the dorsal surface of the brain in the various species of Sipunculus have received but little attention on the part of zoologists. Andreae and Ward mention them, and the former states that they appear to be hollow ; this is, however, not the case. They are comparatively conspicuous objects, and are easily seen when the brain of a Sipunculus is examined through a lens : in |
