ICHTHYOLOGY. 



329 



Geographi- more effect on the progress of Ichthyology. The Museum 

 cal Distri- catalogues of the Serpentiform Apodals, the Lemniscate 

 bution. Apodals, the MormyridcB and Balistidce, contain descrip- 

 ^-*"V™^ tions of a great many species, previously unknown to the 

 world, and present comprehensive views of these groups no- 

 where else to be found. The generic and higher groups 

 they characterize are embodied in our table. We cannot 

 enter further on the bibliography of Ichthyology, and must 

 refer the student to the Bibliographia Zoolof/ica, published 

 by the Ray Society, where he will find all that he wants in 

 this respect. 



ON THE GEOGRAPHICAL DISTRIBUTION 

 OF SPECIES. 



This is a wide field for observation and discussion ; but 

 the way for entering upon it with much hope of success has 

 not as yet been cleared. Systematic Ichthyology is but of 

 recent date ; our acquaintance with the species of fish is as 

 yet limited ; our knowledge of their habits and migrations 

 very imperfect ; and we should only lead to error, were we 

 to attempt to deduce general laws from such scanty data. 

 We can merely therefore glance at a few circumstances 

 connected with "this department of Ichthyology, which, little 

 as it has hitherto been considered, will, when the science 

 has advanced to the proper point, certainly meet with the 

 attention it so fully merits. Temperature has an acknow- 

 ledged influence, both directly and indirectly, on the distri- 

 bution of organized beings over the globe. Vegetation 

 ceases, or nearly so, when we reach the regions of perpe- 

 tual fi-ost, either by ascending lofty mountains, or sailing to- 

 wards the poles -, and even the Protococcus nivalis, that pro- 

 pagates and flourishes in the snow, must owe its gi-owth to 

 the action of the sun's rays, in liquefying a portion of the 

 snow sufficient to furnish fluid for the extension of the 

 simple cells of which it consists. The range of phytopha- 

 gous animals depends, of course, on that of the plants which 

 they can eat and assimilate ; and their distribution again in- 

 fluences that of the predacious kinds which subsist solely 

 or mostly on animalized matter. Migration, though not 

 synonymous with distribution, yet inasmuch as it is an in- 

 stinctive movement, having for its end proper supplies of 

 food, must furnish many facts that bear on the dissemina- 

 tion of species. The extent and character of tie migra- 

 tion varies with he species. Among Mammals it has been 

 Httle noticed, except in the gregarious Ruminants and cer- 

 tain Rodents. The American bison roams over the prairies 

 in quest of fresh grass. When the herbage has gone to 

 seed in one locality, and the haulms are dried up, the vast 

 herds travel onwards till they find a younger and greener 

 vegetation in some district over which a fire has recently 

 run. This movement, whatever may be the extent of the 

 journey over these sea-like prairies, scarcely comes imder 

 the term migration. But the reindeer, pressed by some 

 more recondite instinct, quits the interior where it has fed 

 in winter, and in herds of greater or smaller size, but in 

 numberless succession, and all actuated by a common im- 

 pulse, hastens to the coasts and islands of Hudson's Bay, 

 or of the Arctic Sea. passing rapidly over the intervening 

 barren districts wherein pasture is scanty ; but throughout 

 the march regularly waited upon by bands of wolves. 

 Birds, with their greatly superior locomotive powers, per- 

 form migrations much more remarkable for the length of 

 way. Vast numbers of Anatidtr, natives of the extreme 

 capes and islands of Arctic America, assemble in flocks on 

 the approach of winter, and move southwards to pass that 

 season on the table-lands of Mexico and of Central Ame- 

 rica, lingering on their way only in berry-producing or 

 marshy districts and coasts, and passing over the others 

 high in the air, and with great velocity. The annual mi- 



TOL. XII. 



grations of the Swallows are no less extensive than those of Geographi- 

 the Natatores, and are as evidently designed to secure an '^^^ Distri- 

 appropriate succession of food. Every species has its pro- ^'^''°°\, 

 per range, that of some being of much greater extent both ^'"-■'^^ 

 northwards and southwards than others. Of the Reptilian 

 class, the algivorous Chelonians resort in numbers to cer- 

 tain solitary and sandy shores, for the purpose of depositing 

 their eggs, but there is, as far as we know, no extensive 

 migration of any member of that class in search of food. 

 The Pimiolheres, a family of Crustaceans, also assemble 

 annually in multitudes, descend fi-om their usual places of 

 abode in the interior, and travel in a straight line to the 

 sea, to deposit their eggs in the sand of the shore. It is 

 questionable whether any kind of fish makes long migra- 

 tions either to seek for food or to deposit its eggs. Her- 

 rings have been said to do so, and to issue from their polar 

 retreats to visit their proper spawning places on the coasts 

 of Scotland ; but as regards the length of their journey, this 

 is probably a mistake, though there can be no doubt, that 

 in common with many other fishes, they seek the shallow 

 waters at spawning time ; and it is true also, that the com- - 

 mon Herring exists in the arctic seas, but it is precisely in 

 the spawning months that it has been taken off the arctic 

 shores of America, as well as in the British friths. 



In respect of the power of making long journeys, many 

 fishes are as favourably endowed as the swiftest bird,— their 

 muscular powers are as great or greater, and the medium 

 in which they move is more nearly equal to their bodies in 

 gravity. Whoever has seen the Dolphin {CoryphcBna) ac- 

 companying for days together a fast-sailing vessel running at 

 speed before a fresh trade-wind, and occasionally shooting 

 ahead, or playing round her as if she were at anchor, can have 

 no doubts about the velocity with which a fish can travel. 

 It has been calculated, indeed, that the Salmon can travel 20 

 miles an hoiu- against the stream, and that the Tunny or 

 ('ori/phcena would encircle the globe in a few weeks. This 

 shows us, that unless the diffusion of a species be limited 

 by other causes, mere distance is no obstacle to very many 

 fishes. A bird in its migratory flight can soar high, and 

 take advantage of the upper or lower currents of the air 

 that may be favourable for its course, while at the same 

 time it carries along with it the temperature of the colder 

 regions it has left; "the tenuity of the atmosphere being in 

 fact the limit to its ascent. In the same way a northern 

 fish might find at a distance from the surface the mean 

 temperature of the sea (39°-5 Fahr.) ; its descent into the 

 bosom of the ocean being limited by the pressure it can 

 bear. This line of mean temperature varies in its depth 

 with the latitude. Sir James C. Ross found it to be, in S. 

 Lat. 43 degrees, 3600 feet below the surface ; and in the 

 equatorial and tropical regions 13,000 feet, the surface heat 

 being in the latter districts 78°. In 70 degrees of south 

 latitude, the surface heat is 30° Fahr., and the mean heat of 

 39°-5 has descended 4200 feet. 



The obstacles that are likely to arise to a long journey 

 by any fish, and also to the spread of the species, will vary 

 with its habits. Ground fish, organized for swimming near 

 the bottom only, and feeding there, will be stopped by great 

 depths of the ocean as effectually as a land animal would 

 be by a high mountain range rising far into the snowy re- 

 gions, — they would neither be able to endure the pressure 

 they would have to encounter at great depths, nor the pri- 

 vation of food to which they would be exposed in following 

 the bottom to a depth to which they were not accustomed. 

 James Forbes, whose early death has deprived Natural 

 History of one of its most able and successful cultivators, 

 has shown that marine life diminishes with the depth, 

 and at length ceases, not perhaps at the limit he was in- 

 clined to assign to it, but still in a manner analogous to the 

 ascent of a mountain. To favour the spread of ground- 

 fish, then, a chain of sand banks, submerged to the proper 



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