5-32 FISHES. 



ual, and as these members will be mentioned repeatedly in the follow- 

 ing pages, I will briefly describe them. 



Beo-inning at the head and following the line of the back, we come 

 upon a fin called from its position the "dorsal" fin. In very many 

 species there are two such fins, called, from their relative positions, the 

 first and the second dorsal fins. The extremity of the body is furnished 

 with another fin, popularly called the tail, but more correctly the "cau- 

 dal " fin. The fins which are set on that part of the body which cor- 

 responds to the shoulders are termed the " pectoral " fins ; that which 

 is found on the under surface and in front of the vent is called the 

 " abdominal " fin; and that which is also on the lower surface, and 

 between the vent and tail, is known by the name of the "anal" fin. 

 All these fins vary extremely in shape, size, and even in posi- 

 tion. 



The gill-cover — or operculum, as it is technically called — is sepa- 

 rated into four portions, and is so extensively used in determining the 

 genus and species that a brief description must be given. The front 

 portion, w liich starts immediately below the eye, is called the " prse- 

 operculum," and immediately behind it comes the "operculum." Below 

 the latter is another piece, termed from its position the " sub-opercu- 

 lum," and the lowest piece, which touches all the three above it, is 

 called the " inter-operculum." Below the chin, and reaching to the 

 sub-operculum, are the slender bones termed the " branchiostegous 

 rays," which differ in shape and number according to the kind of 

 fish. 



The scales with which most of the Fish are covered are very beauti- 

 ful in structure, and are formed by successive laminae, increasing, there- 

 fore, in size according to the age of the Fish. They are attached to 

 the skin by one edge, and they overlap each other in such a manner as 

 to allow the creature to pass through the water with the least possible re- 

 sistance. The precise mode of overlapping varies materially in different 

 grncra. Along each side of the Fish runs a series of pores, through which 

 passes a mucous secretion formed in some glands beneath. In order to 

 permit this secretion to reach the outer surface of the body, each scale 

 upon the row which comes upon the pores is pierced with a little tub- 

 ular aperture, which is very perceptible on the exterior, and constitutes 

 the " lateral line." The shape and position of this line are also used 

 in determining the precise position held by any species. In comparing 

 the scales taken from different Fishes, it is always better to take those 

 from the lateral line. 



The heart of the Fish is very simple, consisting of two chambers 

 (|nly, one auricle and one ventricle. The blood is in consequence 



The hearing of Fishes appears in most cases to be dull, and some 



