| OCR Text |
Show 1900.] NEMERTEANS FROM TORRES STRAITS. 829 CEREBRATULUS HADDONI, n. sp. (Plate LV. figs. 7 a-e, 8, & 9.) About 5 cm. of fragments of a single specimen from Thursday Island. The oesophageal region is round and about 6 m m . in diameter. In the intestinal region the breadth is about 8 mm., the depth being 5 m m . The mouth is large. The head-slits extend backwards to the level where the mouth commences. Colour in the preserved state whitish grey, covered with darker mottlings except on the snout. The epithelium in the oesophageal region contains a few large granular cells (Stabcbenzellen) in its deeper portion. There is no well-marked basement-membrane. The cutis presents the fine circular and longitudinal muscle-fibrils. The cutis-glands are poorly developed. The connective-tissue layer (fig. 8, cu.) is very strong, being almost as thick as the powerful external longitudinal muscle-layer. It contains a very few muscle-fibrils. The muscle-layers are all well developed. The vascular system shows a well-marked head-loop. The proboscis is of moderate size, but presents no muscle-crosses. The proboscis-sheath contains the usual outer circular and inner longitudinal muscle-layers. The latter is more strongly developed ventrally than dorsally. Tbe alimentary canal possesses a wide, shallow, ventral gutter in the intestinal region. The excretory system starts some way behind the mouth and extends over about 2 m m . in the preserved specimen (fig. 9). I have been able to observe no openings to the exterior1. The oesophageal vascular lacunas are very small. The excretory tubules lie w7holly ventral to the level of the side stems. The generative sacs are small, numerous, and scattered in the intestinal region, thus not conforming to the usual arrangement, in which there is a single sac between each successive pair of intestinal pouches. Apparently the ducts are not yet developed. In the nervous sgstem the brain presents no special features. Neurochord-cells are not present at tbe level of the ventral commissure. The median dorsal nerve is not distinguishable from the rest of the nervous sheath surrounding the circular musculature. A n inferior median dorsal nerve, lying just above the proboscis-sheath, is well marked in this species. The cerebral organ is seen in section before the separation of the dorsal and ventral lobes of the dorsal ganglion (fig. 7 b). It is invested by gland-cells only on its ventral surface. The head-slits are deep, reaching almost to the brain. Externally they end abruptly before the level where the cerebral organ commences (fig. 9). Eyes and frontal organ are both absent. The head-glands are very scanty and end early. 1 Cf. C. robustus (Punnett, 6), which this species greatly resembles with regard to its excretory and vascular systems. |
