846 MR. GULLIVER ON THE ANATOMY [ Dee. 6, 
noted a measurement of small corpuscles of Ammoccetes for an 
average. 
Man; diameter ofthe disk”... 277 oo coe. oe as 
Sunthickness:ofbhedisk:.sShcy<aiidiecons chearet ae TEabi 
», diameter of pale globules........ sana 
Lamprey, diameter Obst esaiskce oc4-bescicks sheets ah 
: a : 
5 thickness of the disk............ Eva a 
= 1 
4g diameter Of Nucleus. a. . --5 © 0-2 asiaces — 
3 diameter of pale globules .. sain 
Fins. 
Fin-rays.—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 diffi- 
cult 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, espe- 
cially 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 the 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 51, 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 3,455 of an inch in diameter. Each fin- 
ray has a sheath of longitudinal fibres that have elongated nuclei. 
Marginal Papilia, 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 5{; of an inch, and 
half that breadth ; and they are thickly sprinkled with black pigment- 
granules. In P. fluviatilis the marginal papille are smaller and 
fewer than in P. planeri. 

Eye. 
Lens-fibres.— Since the discovery, by Brewster, of the deeply in- 
dented 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 
