434 VERTEBRATA. 



to 1)0 Olio. 'I'll.' lirM.l l.cars a pair --f oyos ; the m.-utli is (lestitiitc of jaws, but is summndod by 

 a mimlxT of .■arfila<:iii"us [...ints. 'I'll.- circulation <>f the blood is eftccted entirely by the eou- 

 tractile force of the arteries ; the blo,.d itself, unlike that of all other vertebrata, is perfectly color- 

 loss. This creature lives in sandy y-rouud at a depth of between ten and twenty fathoms water. 

 It is verv tenacious of life, sid)sisting- f)r liours out of water; it dislikes the light, and bears 

 han.llinii without injurv. It has been frequently taken on the British coasts, and has excited 

 t'roat curiosity by its anomalous sti'iicture. 



Fossil Kisi'ies! — The remains of extinct fishes are exceedingly abundant in various parts of 

 the world. These, with the existing races, have been grouped by M. Agassiz, in his celebrated 

 work, lirchcrchcs siir Ifs Poinsoiin Fossiles, in four divisions, the P/aco/des^ Ganoides, Cfcvoi- 

 rlrs, and C>/cloid(s, these being severally distinguished by the structure of their scales. The 

 term I'laroidcx, including the sharks, rays, ttc, is derived from the Greek ^jZc/j-, a plate or slab, 

 and is applied to the first of these groups on account of the irregularity which the solid tegu- 

 mentary parts present. The Ganoides, from the Greek r/anos, splendor, and embracing the silur- 

 ida\ sturixeoiis, kc, are distinguished by the angular form of their scales. In the Ctcnoidcti, in- 

 chnling the fiat fishes, percid;c, etc., named from the Greek ctenos, a comb, the scales consist of 

 laminie, whose posterior and free margin is pectinated. In the C9/cloidcs, including the bass, 

 cod, salmon, carp, itc, and named from the Greek c//clo.% a circle, the scales consist of simple 

 iamiiue, with th.e posterior margin smooth. 



The nmnbcr of species of extinct fishes in the British Islands alone, noted by M. Agassiz, is 

 over five hundred. Some existing species have no representatives in the older strata. The most 

 ancient of the finny races, in a geological sense, arc the I'lacoid fishes. 



The Artificial Propagation of Fishes. — It has been long known that the eggs of fishes could 

 be taken and transported from one place to another, and there, being placed in water suited 

 to them, would hatch and produce thrifty oflfspring. The Chinese have practiced this for ages, 

 and the ancient Romans conducted it on an extensive scale, in this manner not only stocking 

 natural lakes and streams with various kinds of fish, but also their vast artificial reservoirs. 

 Modern naturalists had gone somewhat farther, ha\ing discovei'cd the mode by which the 

 eggs of fishes are fecundated, that is, by strewing the ova of the female with the milt of 

 the male. No attempt, however, appears to have been made to take practical advantage of this 

 fact, and to render the artificial breeding of fishes a general system of national economy, till 

 within a few years. In 18-30 the attention of the French Government was called to the opera- 

 tions of two illiterate but ingenious fishermen, Messrs. Gehin and Rciny,"^ in the littla village of 

 Brcsse, on the eastern borders of France, among the Vosges Mountains, who, as it appears, of 

 themselves, and without instruction, conceived and put in practical operation the artificiul brjcd- 



* The history of (lie proceedings of Gchin and Uemy is thus given in Mr. Fry's excellent and interesting work : "As 

 long ago as 1841, they commeuced to observe carefully the habits of tho trout, and in the month of November of that 

 ye:ir, during a full nioun, tliey passed night and day on the bank of a river, never for an instant losing sight of these 

 fish, and watching most intently all their i)re]iaratious for laying and preserving tlieir eggs. 



" The results of their observations were these : 



" The trout come together in a fjhoal, and choose a cnrrent with a gravelly bottom as the best i -lace to lay their 

 eggs. They dig in it a round hole, sometimes of tke d-^pth of several inches by three feet in diameter: they place 

 in the middle of (hij .space, parallel vilh the cuiTcnt, a line of stones, the size of which varies with Ibj .si::j of the 

 fish. 



" The female then passes over f he lino of stone^-, .gliding over, rnljbiiig against or resting upon them. Tlii i .s'.iu does 

 again and again, some tv,-cnty or thirty limes, (ill her eggs are all laid i;i the crevices of the gravel. 



'• V\ hen t.iefjmak-ha3d)ne this, the male, in the same manner, by passing over and pressing upon th;i gravel, omits 

 the milt, or soft roe, v.-hieh covers and fccandatc.i the egg;; fien v,-i(h tail, fins, licid, and belly ha works r.way till 

 he manages to cover the eggs with gravel. 



" N'ow a second female commences, and in t'.ie r.amc manner 1 ;ys her eggs in a parallel line with and against the first 

 row. When the fecundation i ; complete, which ii generally ii about fifteen days, according t) the nnmbcr of fish, all 

 unite in heaping up ctone; and gravel in mounds upon the c^'^^, in a manner resembling the great ant-h!!Li tliat may 

 be found near by. 



" Mr. Gehin believe--, that their mason- -.vor'.c U, in a manner, cemente 1 by a slimy secretion, with which they cover 

 the stones, while incessantly rubbing over and jjressing against them in heaping tliem up ; fjr he foimd it dilficult to 

 destroy the moimds s > formed by scratching apart the material with his fin-rers? 



" The eggs remain in this way for a month or two, while the proce3.3 of incubation goes on; at the end of a time, 



