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Show 046 MR. GULLIVER ON THE ANATOMY [Dec. 6, noted a measurement of small corpuscles of Ammoccetes for an average. Man, diameter of the disk . . -- „ thickness of the disk TiTioo ,, diameter of pale globules T^- Lamprey, diameter of the disk r J> 2134 „ thickness of the disk A- 6200 ,, diameter of nucleus A- "„ diameter of pale globules 6-4 o-u FINS. Fin-rags. -The Lampreys, under the head of Dermopteri, are usually described as " without fin-rays;" see, for example, Mr. Couch's recent 'History of the Fishes of the British Islands,' vol. iv. p. 385, and the still later ' Comp. Anatomy of Vertebrates,' vol. i. p. 7. Yet these rays are plainly visible in more than one species of Lamprey, and so thickly set in the dorsal fin that it might be difficult to count them; and according to Prof. Huxley (Introduction to the Classification of Animals, 8vo, London 1869, p. 63), "it is questionable whether any fish exists altogether devoid of the system of median fin-rays." They are easily shown in the Lampreys, especially when the fin-skin is removed by hot water ; and, when a portion of the living fin is cut off, the skin will so contract after death as to leave tbe divided ends of the rays projecting from the cut surface. In Petromyzon planeri the fin-rays at their middle have a mean diameter of about ^fa of an inch, often much more or less ; that from which the drawing (fig. 8, p. 848) was taken was scarcely half as thick; they are most of them split towards their tips; and, like the endo-skeleton, are cartilaginous; the cells of the cartilage compose the whole thickness of the fin-ray, are of a somewhat polygonal shape, mostly oblong, closely packed together, with their long axes across the ray, and each cell is about ^Vo °^ a n 'nc'h ln diameter. Each fin-ray has a sheath of longitudinal fibres that have elongated nuclei. Marginal Papillee, fig. 7, p. 848.--The free edge of the dorsal fin has a pretty fringe of a single row of conical papillae. In Planer's Lamprey they have an average length of about -j^ of an inch, and half that breadth ; and they are thickly sprinkled with black pigment-granules. In P. fluviatilis the marginal papillae are smaller and fewer than in P. planeri. EYE. Lens-fibres.- Since the discovery, by Brewster, of the deeply and interlocking edges of these fibres in the Cod, this has been adopted as a common character of fishes. But the indentations and the diameter of these fibres are so different in diverse species as to afford valuable taxonomic characters in the class. Thus, e. g., while |