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 fish- 

 ing-ground, and so went misanthropically home to his dinner, I called to mind the pro- 

 gression of the Fishes, 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 bal- 

 ancers, 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 in- 

 dividual, 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 ex- 

 tremity 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 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 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 por- 

 tions, and is so extensively used in determining the genus and species that a brief de- 

 scription must be given. The front portion, which starts immediately below the eye, is 

 called the " prae-operculum," and immediately behind it comes the " operculum." 

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

 and 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 that 

 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 in- 

 ternal structure of the ear is moderately developed, and there are some curious little 

 bones found within the cavity, technically called otoliths. 



