332 ' THE PRACTICAL FISHERMAN. 



brain, sight, or some other faculty hitherto undiscovered, may be 

 involved in this curious anatomical puzzle. 



The eye of the eel, indeed, is a peculiarly interesting object under 

 the microscope. It varies in a number of eels from light brown to 

 almost a lavender grey. The iris is, of course, unexpanding, as in nearly 

 all fish ; the reason, probably, is that the diminished light is never too 

 strong for the retina. It has, however, a fine granulated appearance of 

 great beauty. 



Paley ("Natural Theology") has the following paragraph anent the 

 eye of the eel, which is, of course, strictly a physiological fact : 



" In the eel, which has to work its head through sand and gravel, the 

 roughest and hardest substances, there is placed before the eye, at some 

 distance from it, a transparent horny convex case or covering, which, 

 without obstructing the sight, defends the organ. To such an animal, 

 could anything be more wanted or more useful ? " 



Again reverting to the skin of the eel, I may remark that the fish 

 is encased in a most beautiful suit of scale armour, and now and then I 

 have found it possessing iridescent hues of great beauty. The scales are 

 of an oval figure, and when viewed under the microscope with polarised 

 light, are exceedingly brilliant objects. The scales of fishes M. Agassiz 

 divided into four orders, as stated on page 24, which he termed the 

 placoid, ganoid, ctenoid, and cycloid. In the first two the scales are 

 more or less coated with an enamel ; in others they are of a horny nature. 

 To the cycloid belong the herring, the eel, and the carp, and, indeed, most 

 of our edible fish. Generally their scales are laminated and circular, but 

 as to form those of the eel are exceptions. The occasional iridescence is 

 caused by a finely-grooved structure, like that of the skin on the top of 

 an infant's finger, as I have stated in the chapter on Grayling. Sir 

 David Brewster (" Treatise on Optics") was the first to notice this. 

 The iridescence of the pearl is also due to the same cause. Some of the 

 most prismatic, obtained from a species " Mytilus," says Dr. Hogg, 

 " consist of a beautiful purple-coloured series of concentric laminae. 

 That this iridescence is really due to the grooved surface was demon- 

 strated by a Birmingham manufacturer, who cut grooves in steel at 

 distances from -TOO to ooVo of an inch, and produced the same effect in 

 a superlative degree, originating a new manufacture of fancy articles in 

 the shape of buttons, trinkets, &c." 



Dr. Carpenter (" Cyclopaedia of Anatomy ") also refers to the common 

 earshell (HaUotus splendens), and remarks, from certain experiments 

 on its shell, that " the beautiful effects commonly called mother-o'- 

 pearl are produced solely by the disposition of single membranous 

 layers in folds or plaits lying more or less obliquely to the general 



