OCR Text |
Show 828 MR R. C. PUNNETT ON [Nov. 20, procured. Width about 2*5 m m . The head-slits are very long, extending over 5 m m . The posterior 3 mm., however, are very shallow. The mouth commences at about the termination of the deep portion of the head-slits and is about 3 m m . in length. After preservation tbe colour was dark olive-brown. Starting from about *5 m m . from the tip of the snout, a paler dorsal band about 1 m m . in breadth reached backwards. The epithelium contains a number of large granular unicellular glands in its deeper portion. Beneath the thin basement-membrane is a layer of longitudinal muscle-fibrils in the cutis, and underneath these again are the cutis-glands and the connective-tissue layer of the cutis. Dorso-laterally for a small portion of the circumference, as seen in transverse section, the cutis is modified on each side by the presence of an enormous quantity of what appear to be small rhabdites (fig. 4, rh.). They take a very vivid colour with picric acid, and may easily be traced through the cutis-muscles (mlc), the basement-membrane, and the epithelium. The muscle-layers show no special features. There is no diagonal layer. In the vascular system there is a well-marked head-loop. It was not possible to fix definitely the point of exit of the dorsal vessel, as the fragment cut only just included the excretory system. At this level the vessel still ran in the sheath. The proboscis was lacking. The proboscis-sheath shows the usual inner longitudinal and outer circular muscle-layers. The excretory system commences at the posterior limit of the cerebral organ (fig. 5). It lies wholly dorsal to the level of the side steins. There is a single duct on each side near its middle portion. In the nervous system the median dorsal nerve is well marked. The dorsal commissure in the brain is very posteriorly situated, not being given off until after the separation of the dorsal from tbe ventral ganglia. Neurochord-cells are present at the level of the ventral commissure. The dorsal lobe of the dorsal ganglion is large. The brain as a whole is much flattened, as, indeed, is the whole of the fragment by which this species is at present represented. The cerebral organ is elliptical in shape, being flattened dorso-ventrally. Gland-cells are found above and below (fig. 2 c-e). A portion open into the ciliated canal before it joins the dorsal ganglion (tig. 2 a). The frontal organ is well marked. Eges are probably absent. The head-glands are very short and soon become fused with the cutis-glands. This species bears some resemblance to that described by Burger (1) under the name of Cerebratulus spadix, but seems to be distinguished from it by the vascular head-loop and by the fact that tbe mouth commences before the termination of tbe cerebral organs. The curious agglomeration of rhabdites also seems peculiar. |