OCR Text |
Show 1903.] MEDUSA FROM BRITISH COLUMBIA AND ALASKA. 175 situated on an elevation on the outer side of the tentacle-base, where the latter leaves the margin of the bell. No otocysts are present. The stomach rests with a small angular base on the gelatinous peduncle, receiving at this level the radial canals. It then widens into a pouch, becoming again constricted into the proboscis which bears the mouth below. In the living condition the digestive cavity is circular in outline. In the distended condition it looks thin-walled. The mouth has four short lobes which turn outward. Each lobe is again lobulated or coarsely toothed. The four radial canals are well marked, cylindrical tubes running direct in their course. They pass from the angles of the stomach upward along the peduncular cone to the highest point of the subumbrellar space and then descend directly to the circular canal of the bell-margin. Along the whole course of these radial canals short lateral diverticula are given off, the ends of the canals alone being free from them. Only a relatively small number of diverticula on one side of a radial canal are placed opposite those on the other side of the canal. None are branched or have their ends enlarged in a club-shaped manner. On either side of each radial canal there are about 32 of these diverticula. They are shorter near the ends of the radial canals, where these approach the bell-margin being mere protuberances. Gradually towards the middle of the bell they increase in length, until they measure about twice the diameter of a radial canal in length. The gonads are long finger-shaped processes dependent from the proximal part of the radial canals, the part most free from diverticula. There are eight gonads in each of the four groups, the central ones being the longest and reaching to the level of the velum. The outer shorter gonads may be mere rudiments. The latter cannot be mistaken for diverticula, being thicker and hanging free in the subumbrellar cavity. There are a few small diverticula on the radial canals over the region where the gonads are attached. Colour.-Transparent and colourless except the gonads and tentacles, which are tinged a pale yellow in preserved material. Habitat.- Puget Sound, collected by Kincaid. Discussion.-In Agassiz's figure (2) of P. penicillata only 22 of the diverticula are on an average arranged opposite one another on the sides of the radial canals. It is very doubtful if any importance can be attached to the position of these diverticula; certainly their opposite arrangement is unworthy the generic importance assigned it by Haeckel (18). In the generic diagnosis, p. 149, he says of the radial canals of Polyorchis: " . . . . im Distal-Theile mehrere Paar von gegenstandigen geschlechtslosen Fiederasten tragen." Both Eysenhardt & Chamisso (12) and Eschscholtz (11) represent the diverticula on the course of the radial canals, in their figures of these Medusa?, by cross-lines drawn at right angles to the canals; this produces the appearance |