246 On the Scales of Fishes. 



these two regions, now so widely separated, were linked, toge- 

 ther by an intervening band of tropical land. In no other way 

 can we account for the presence of Barbets and. trogons in the 

 tropics of each hemisphere. It is hardly possible to imagine 

 that the common ancestors of these two families, which from 

 their whole organization are essentially denizens of the tropics, 

 were themselves extra-tropical. In the case of the parrots, 

 however, we have probably to deal with a very ancient and 

 long-enduring stock, which may have been formerly cosmo- 

 politan,* and members of which are even now found in the 

 temperate regions of the southern hemisphere. 



ON THE STRUCTURE AND MANNER OF GROWTH 

 OF THE SCALES OF FISHES. 



BY JONATHAN COUCH, F.L.S., C.M.Z.S., ETC. 



Op the vast number of the known species of fish, amounting 

 to several thousands, a large proportion have the body covered, 

 and in numerous instances the head also, with scales ; which, 

 for the most part, are so arranged, as to form an armour of 

 defence, as well as an adornment of beauty, that grows with 

 their growth without an increase of number, and by its per- 

 manency differs in essential properties from those scales — not 

 very unlike in appearance, and even in some of their uses — 

 which clothe the bodies of reptiles ; but which latter, when 

 once formed, are incapable of growth. To enable them to be 

 accommodated to the increase of bulk of the animal, these 

 latter must be thrown off, together with the skin that bears 

 them, to be succeeded by another crop, which is altogether 

 new — a circumstance that does not take place in any species of 

 fish with which we are acquainted. There is, therefore, a 

 much closer relationship between the scales of fishes, of which 

 we have now to treat, and the spines and plates, however 

 otherwise unlike, which we find scattered over or covering the 

 bodies of some other families of fishes, especially as regards 

 their mode of increase in size — a fact to which, on another 

 occasion, our attention will be directed, as showing an example 

 in which an apparently different result is obtained by a simple 



* Groups of general distribution over tbo whole world's surface, such a9 the 

 falcons (Falconidcz), and the ducks (Anatidce), are called " cosmopolitan." Groups 

 confined to the tropics, rich as the barbets, trogons, and parrots, may be called " tro- 

 picopolitan." Another class of natural groups is confined to the northern portion of 

 each hemisphere, and may be termed " arctopolitun." Such are the awks (Alcidee) 

 and the grouse (Tetraonidcp). 



