FINS, SCALES. GILL-COVER, CIRCULATION AND HEARING. 197 



with a party of friends on board a fishing barge in a small lake, and deserted by an ill- 

 conditioned boatman, who refused either to put us ashore or take us to a better fishirig- 

 grcund, and so went misanthropically home to his dinner, I called to mind the progres- 

 sion of the Pishes, and straightway became independent of the boatman. After hauling up 

 the anchor, I inserted the butt end of the largest fishing-rod into the head of the rudder so 

 as to form an extempore tiller, and by moving the rudder gently to and fro I was able to 

 propel the barge in any direction and to any distance. We thus traversed the lake at our 

 pleasure, drove the barge ashore at its further extremity, and left the boatman to find it 

 and take it back as he could. 



Even the eels and the flat Fishes, with their gracefully serpentine movements, adopt 

 this mode of progression, though it is not so apparent as in the Fish whose bodies are less 

 flexible and accordingly employ more force in the tail itself. 



The fins are scarcely employed at all in progression, but are usually used as balancers, 

 and occasionally to check an onward movement. Before proceeding further, I may 

 mention that all the fins of a Fish are distinguished by appropriate names. As they are 

 extremely important in determining the species and even the genus of the individual, and 

 as these members will be repeatedly mentioned in the following pages, I will briefly 

 describe them. 



Beginning 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 

 caudal fin. The fins which are set on that part of the body which corresponds 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 the tail, is known by the name of the " anal " fin. All 

 these fins vary extremely in shape, size, and position. The figure on page 198 exhibits 

 all these fins. 



The gill-cover, or operculum as it is technically called, is separated into four portions, 

 and is so extensively used in determining the genus and species that a brief description 

 must be given. The front portion, which 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-operculum," 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 beautiful in structure, 

 aud are formed by successive laminae, increasing therefore 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 

 resistance. The precise mode of overlapping varies materially in different genera. 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 tubular 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 only, one auricle 

 and one ventricle. The blood is in consequence cold. 



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

 that they are totally destitute of this faculty. It is now, however, known tnat many 

 species have been proved capable of hearing sounds, and that carp and other fish can be 

 taught to come for their food at the sound of a bell or whistle. The internal structure of 

 the ear is moderately developed, and there are some curious little bones found within the 

 cavity, technically called otoliths. 



