104 



Introdl'Ction.- 



-FISHES.- 



-Cl.vssification. 



who, unable to draw up a recognizable description, Lave 

 ■whetted the curiosity of naturalists, but have left the 

 species which chance had placed in their bauds to hold 

 an uncertain niche in our systems. 



A general acquaintance witli the principal facts of 

 ichthyology is of national importance to a maritime 

 country like Great Britain, with an increasing population 

 and a limited area of arable land. At the present time, 

 the cost of fish renders it lather a lu.xury for the rich tlian 

 food for the masses; but there is no doubt that, not- 

 withstanding tlie number of people at present employed 

 in catching, curing, and carrying fish to the markets, 

 this source of food might be incalculably extended. We 

 are still behind the Dutch and Biscayans in some of 

 the fisheries carried on in the narrow seas ; and Europe 

 at large is vastly surpassed by the Chinese in the 

 skill with which supplies for a teeming population are 

 extracted from the ocean, or in the economical rearing 

 of fish in every pond ; a sheet of water in China being 

 made as productive of food as the same extent of good 

 arable land. Of late years cod-liver oil, having been 

 ascertained to be a most valuable remedy against the 

 national malady consumption, has already become an 

 extensive article of trafiic ; and very recently, experi- 

 ments made in France have shown that oil obtained 

 from the livers of sharks is not less useful in the same 

 disease. Now in JIarch, 1858, wdien an unbroken 

 scull of one kind of shark (the Picked Dog-fish) beset 

 the northern coasts of Scotland, and extended twenty 

 miles out to sea, filling every harbour and bay — had 

 proper fisheries been establislied, not only might an 

 incredible quantity of high-priced oil have been pro- 

 cured, but vast stores of sharks' fins might have been 

 prepared for export to China, where they are in great 

 request for the purpose of making excellent soup. It 

 is, perhaps, too much to expect that Englishmen should 

 lay aside their prejudices, and learn from the Chinese 

 the modes of converting parts of these fish rejected by 

 our fishermen as useless, into palatable and nourish- 

 ing food. Not from the observations of our own 

 seamen, but from researches made by order of the 

 Dutch government, have we learnt that the Herring 

 fishery is productive in those parts of the sea onl}', 

 whose temperature ranges between bi" and 58° of 

 Fahrenheit's thermometer. 



Agassiz, a most important authority in classification, 

 has carried the subdivision of the vertebrate animals 

 further than his predecessors, and distributes the 

 Fisiiics, as defined above, into four classes, viz : — 



1st. Myzontes, composed of two orders, Myxinoids 

 and Ci/dostomes. 



2ud. Fishes Proper, of two orders, Clenoids and 

 Cycloids. 



3rd. Ganoids, of three orders, Calacanihs (fossil), 

 Acipenso-oids, and Sauroids, with the addition of other 

 three orders, whose true position is to be ascertained 

 by future research : these are Siluroids, Plccto/jnalhs, 

 and Lnphobranchs. 



4th. Selachians, of three orders, Chimaroids, 

 Galeodcs, and Batidcs. This arrangement, considered 

 to be in part provisional, and depending on the result 

 of investigations now in progress, is not adopted in 

 the ensuing pages, though occasionally referred to ; 



the fishes being ti'eated in this work as a single class, 

 having a common character — the oxygenation of the 

 blood by air diffused in water. 



Professor Owen has recently taken a very different 

 view of the arrangement of the inferior vertebrals from 

 the above, and proposes to unite the Fishes, Amphi- 

 bians, and Eeptiles into one class, which he names 



II.EMATOCKVA. 



" Oar little systems have their day ; 

 They have their day and cease to bo ; 

 They are but broken lights of Tlice^ 

 And thou, Lord I art more than they." 



— Tennyson, In Mem. vi. 



That a correct knowledge of the structure and 

 development of any group of animals is as necessary 

 to the zoologist as an acquaintance with their phy- 

 siognomy and habits, is so evident, that it seems 

 unnecessary to atfirm that no one can hope to become 

 an accomplished ichthyologist unless he submits to the 

 labour of patient anatomical investigation. For reasons 

 already assigned, however, the notices of structure will 

 not be extended in this work beyond what is requisite 

 for explaining the terms used in characterizing the 

 orders and family groups. 



Scales. — In some fishes scales are not developed, 

 the skin being generally in that case thick, smooth, 

 and slippery, owing to the abundance of defensive 

 mucus secreted by its nmnerous glands. Comparative 

 anatomists distinguish the internal more or less firm 

 framework by the name of endo-skeleton, from the 

 external or exo-skeleton, which is intimately connected 

 with the skin or developed in its textures, and is 

 therefore sometimes called the dermal s7,:eleton. The 

 Myzo7ites o( AgSiSs\z,or Da-mojileres, furnish an instance 

 of an entire order (or, as the author just named con- 

 siders them to be, a whole class) destitute of scales, and 

 with so little approach to the secretion of bony matter 

 that systematic authors call the eso-i;keleton " muco- 

 dermoid," or indurated mucus secreted from the skin, 

 the internal skeleton at the same time being cartilagi- 

 nous or membranous. Almost all the otlier great groups 

 of fishes contain some species without scales, but allied 

 by the rest of their structure to the scaly fishes with 

 which they are classed. Scales, when present, originate 

 in a little pouch of the external skin, technically named 

 a follicle, and resembling the fold of the gum from 

 which tlie germ of a tooth is evolved. Agassiz, when 

 studying fossil fishes, was led to distinguish four kinds 

 of scales, wdiiob he termed cycloid, ctenoid, ganoid, and 

 jilacoid. 



Cycloid scales are smooth on their discs and edges, 

 but when examined through a lens, exhibit numerous 

 concentric lines, variously flexed, yet having always 

 a certain relation to the border of the disc. Most 

 generally in that part of the scale which remains in 

 the follicle, and is covered by the scale immediately 

 before it, these lines of structure by dipping and undu- 

 lating produce furrows radiating like the sticks of a 

 fan. In all the most important groups of those fishes 

 which are clothed with cycloid scales, the bones of the 

 skeleton contain I'adiated or fusiform bone corpuscles.* 



* KuUikcr, Troceedings of the Koyal Society, is. p. G56. 



