OCR Text |
Show 1887-] NEW GENUS OF LUMBRICID.E. 159 rather than protruded, and the segments of the body in most instances were perfectly normal and not unduly contracted. The gizzard is like that of other Earthworms. ^Esophageal Glands.-Behind the gizzard and in front of the intestines the oesophagus is furnished with certain glands, which are evidently the homologues of similarly placed glands in other Earthworms. These glands are kidney-shaped and lie on the dorsal or lateral aspect of the oesophagus, with the concave side turned towards the oesophagus; at the middle of its concavity the gland is connected with the oesophagus by a short duct. The general appearance of these glands is strikingly similar to the " kidney-shaped glands" which I have described1 in the intestinal region of Megascolex caruleus; apparently they also resemble in outward appearance the oesophageal glands of Notoscolex camdenensis'2, though frequently the oesophageal glands of Earthworms have not this peculiar shape. The oesophageal glands of Thamnodrilus are furnished with a very abundant blood-supply. This blood-supply is derived from the supraintestinal trunk, and not from the dorsal vessel; in the case of the two posterior pairs, at any rate, of these glands, a branch is given off on either side from the supraintestinal vessel ; this at once divides into two trunks ; the inner branch goes to the septum and ramifies upon its surface; the outer branch conveys blood to the oesophageal gland, which it reaches by passing along the pedicle by which that gland is attached to the oesophageal walls ; the vessel then breaks up into a network of capillaries on both the anterior and posterior surfaces of the gland. It is important to notice that in these segments both the dorsal region of the mesentery and the oesophageal gland are supplied with blood from the supraintestinal trunk ; the dorsal vessel gives off no branches in these segments. In Urochata the calciferous glands have, according to Perrier, a similar blood-supply. There were altogether six pairs of these glands situated in segments 9-14 ; the last two pairs, i. e. those situated in segments 13 and 14, were situated nearer to the doisal surface of the in-testine than those which preceed them. The number of those glands (six pairs) is unusual, three being the almost constant number of pairs in other Earthworms; in certain species of Perichata, however, there appear to be as many as six pairs of oesophageal glands. Body-cavity.-The dissection of this part of the body was rendered very difficult by the toughness of the septa in this region and by their firm connection with one another by numerous tendinous threads; these septa, however, in Thamnodrilus, are not specially thickened, as thev are in many other Earthworms, but are thin and transparent, as in the posterior region of the body. The body communicates with the exterior only by the apertures of the nephridia ; there are no dorsal pores present. 1 Trans. Roy. Soc. Edinb. vol. xxxii. 2 Proc. Linn. Soc. N. S. W . 1886, pl. viii. fig. 1, i.g. |