TIw Fish World at Rome. 225 



bo the extreme depression. The English Channel, east of 

 Eddystone, is not more that 50 fathoms; but on the west, 

 coast of Ireland, Dr. Harvey tells us, a depth of 300 to 400 

 fathoms is soon attained. As a rule, the sea-bed, within a 

 a moderate distance from the shore, partakes of the geological 

 character of the formations on the coast ; and if a fish swam 

 from the granites and slates of Cornwall to the chalk of Sussex, 

 he would find the peculiarities of the watery region changing 

 very much like those on the land. Such, then, are a few par- 

 ticulars of the localities in which fish existence is carried on. 

 As on dry land, the plants nourish certain kinds of animals, and 

 the strong devour the weak according to the various methods of 

 predaceous life ; but there is this difference between terrestrial 

 and marine vegetation, that the latter derives nearly all its 

 nutriment from the fluid element, as its roots are, for the most 

 part, only anchors and supports, and not also a machinery for 

 the absorption of food. Thus the water, with the various 

 saline, earthy, and other elements that it holds in solution, 

 forms the foundation of the entire mass of existence whichit 

 contains. 



If we pass from the consideration of where the fish lives, to 

 the inquiry of what the fish is, we find it to be, in the words of 

 Dr. Grant,* " a cold-blooded, oviparous, branchiated animal, 

 with one auricle and one ventricle of the heart, not under- 

 going metamorphosis, covered with scales, and having the 

 arms and legs constructed as fins, for a permanent residence in 

 the waters. The rudimentary lungs (air-bladders) are very 

 rarely employed for breathing, generally for regulating their 

 specific gravity. They mostly impregnate the ova externally, 

 aud there is no amnion or allantois in the ovum." To this 

 brief description some particulars must be added, for, in the 

 words of Mr. Couch, " in a fish the whole mass of blood passes 

 through the gills for the purpose of receiving the influence of 

 the air contained in the water, without being again returned to 

 the heart, until it has been carried to the other parts of the 

 body/' 



The heart of a fish is thus devoted to the respiratory cir- 

 culation. In the reptile, which stands in zoological rank higher 

 than the fish, the heart has three cavities — a single ventricle, 

 and two auricles ; but breathing air direct, by means of lungs, 

 and passing much of its time in torpor, or repose, it does not 

 need that all its circulating fluid should be exposed to the 

 respiratory process before traversing its body; and hence 

 one portion of aerated blood from the lungs, is mingled 

 with another portion of venous blood which has not passed 

 through them, and this mixture is sent out by the single ven- 



* Tabular View of the Primary Divisions of the Animal Kingdom. 



