1892.] MR. R. H. BURNE ON MYXINE GLUTINOSA. 70/ 



In Bdellostoma I found that in the main it answered very well to 

 Miiller's figure and description, although it is apparently liable to 

 vary in shape, as will be seen by referring to my drawings (see Plate 

 XL VI I. figs. 5 and 6, which represent the cartilage as present in the 

 two specimens I dissected). Fig. 6 corresponds very much to Miiller's 

 drawing ; fig. .5, however, although constructed on the same triradiate 

 plan, is a good deal more complicated by means of angles and 

 processes ; tliis variation in shape is still more marked in Parker's 

 figure \ None of the true gill-tubes on either side had any supporting 

 skeleton. "We 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 aud clearing the gill- 

 tubes of fat, a small piece of cartilage (fig.l, A, Plate XLVIL) 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 oi Bdello- 

 stoma ; the relations of the fourth ray (figs. 1 & ?>, B), however, point 

 it out as being somethini< different, for, leaving the cutaneo-ceso- 

 phageal 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 con- 

 siderably 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 sling- 

 like 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 branciiial basket oiPetromyzon 

 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 Gegenbaur ". 



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.". 



^ Gegenbaur, Jenaische Zeitschrift, v. 1870, p. 49. 



