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Show 1892.] MR. R. H. BURNE ON MYXINE GLUTINOSA. 707 In Bdellostoma I found that in the main it answered very well to Midler's figure and description, although it is apparently liable to vary in shape, as will be seen by referring to m y drawings (see Plate XLVII. figs. 5 and 6, which represent the cartilage as present in the two specimens I dissected). Fig. 6 corresponds very much to Midler's drawing ; fig. 5, however, although constructed on the same triradiate plan, is a good deal more complicated by means of angles and processes; this variation in shape is still more marked in Parker's figure \ None of the true gill-tubes on either side had any supporting skeleton. W e may say, then, with regard to Bdellostoma, that the branchial basket is represented upon the left side only by a small plate of cartilage, usually more or less triradiate, supporting the anterior dorsal wall of the cutaneo-oesophageal duct. Let us now consider the branchial basket in Myxine glutinosa. Upon removing the body-wall on the left side and clearing the gill-tubes of fat, a small piece of cartilage (fig.l, A, Plate XLVII.) can be seen lying on the lateral wall of the cutaneo-oesophageal duct; it may be said to consist of a rectangular rod-like body produced at each corner into a ray ; of these the two dorsal and the posterior ventral seem to answer to the three rays of the branchial basket of Bdellostoma ; the relations of the fourth ray (figs. 1 & 3, B ) , however, point it out as being something different, for, leaving the cutaneo-oesophageal duct, it runs forward as a fine bar of cartilage, which bends beneath the confluent gill-tubes, spreading out as it does so into a thin sheet, to form, as it were, a sling for the support of the gill-tubes. On the right side of the animal the structural conditions are considerably simpler, owing chiefly to the absence of a cutaneo-oesophageal duct: the branchial basket here is represented merely by a cartilaginous ring (figs. 2 & 4, C) which surrounds the fused gill-tubes and supports them much in the same way as on the opposite side, the anterior part of the ring being broadened out into a slinglike plate, the posterior being thin and rod-like. The branchial basket of Myxine can be conveniently divided up into two parts : the one, unpaired, related to the cutaneo-oesophageal duct and comparable to the triradiate cartilage of Bdellostoma ; the other paired, and acting as a support to the true gill-tubes. Owing to the small size of this branchial skeleton in Myxine, it is impossible without the microscope to determine whether it is composed of cartilage or no. To be certain upon this point I had some sections of it cut, which upon examination showed precisely the same structure as the cartilage of the branchial basket of Petromyzon fluviatilis; that is to say, a feeble soft form of cartilage, the cells large and varying greatly in size and shape, the cement-substance between them thin-in fact, much the same as the cartilage at the sides of the notochord of the Lamprey described by Gegenbaur2. Although some sort of branchial basket was to be expected in Myxine, yet this, I think, is specially interesting in that, besides 1 L. c. pi. 16. fig. 7. 2 Gegenbaur, Jenaische Zeitschrift, v. 1870, p. 49. |