]60 



ICHTHYOLOGY. 



Introduc- and throat, and the strength of the teeth and jaws. If the 

 tion. teeth are sharp and hooked, they are capable of securing 



^"""Y^*^ tlie slenderest and most agile animals ; if they are broad 

 and strong, they are able to bruise the hardest aliment ; if 

 they are feeble or entirely wanting, they are only service- 

 able in procuring some inert or unresisting prey. Fishes 

 indeed show but little choice in the selection of their food, 

 and their digestive powers are so strong and rapid as to 

 suffice to dissolve very speedily all kinds of animal sub- 

 stances. They greedily swallow other fishes, notwithstand- 

 ing the sharp spines or bony ridges with which they may 

 be armed ; they attack and devour crabs and shell-fish, 

 gulping them entire if they cannot otherwise attain their 

 object ; they do not object occasionally to swallow the 

 young even of their own species, and the more power- 

 ful kinds carry their warfare into other kingdoms of na- 

 ture, and revel on rats, reptiles, and young ducklings, to 

 say nothing of the ferocious shark, which not seldom 

 makes a meal even of the lord of the creation. The spe- 

 cies which Hve chiefly on vegetable substances are few in 

 number. 



The growth of fishes depends greatly on the nature and 

 supply of food, and different individuals of the same species 

 exhibit a great disparity in their respective dimensions. 

 They grow less rapidly in small ponds or shallow streams, 

 than in large lakes and deep rivers.' The growth itself 

 seems to continue for a great length of time, and we can 

 scarcely set bounds to, certainly we know not with preci- 

 sion, the utmost range of the specific size of fishes. Even 

 among species in no way remarkable for their dimensions, 

 we ever and anon meet with ancient individuals, favourably 

 situated, which vastly exceed the ordinary weight and mea- 

 surement of their kind. 



The teeth of fishes are sometimes spread over all the 

 bones which envelope the cavities of the mouth and pha- 

 rynx; on the maxillary, inter-maxillary, and palatine bones ; 

 on the vomer, the tongue, the branchial arches, and pha- 

 ryngeal bones. In certain genera thf;y exist on all those 

 parts ; while in others they are wanting on some, or are 

 even entirely absent on all. The denominations of the 

 teeth are derived from their position, that is, from the 

 bones to which they are attached, and are consequently as 

 numerous as the varieties of their situation. Their forms 

 are not less varied than their stations, and give rise to 

 terms still more numerous. The majority are conical or 

 hooked, more or less acute. When these hooks are in con- 

 siderable number, and disposed in several rows, or in quin- 

 cunx, they are compared to those sharp points which beset 

 the instruments called cards, used in the working of wool 

 or cotton. It is to this form and distribution that we allude 

 in the descriptive portion of the present treatise when we 

 happen to use the French term en carde. Sometimes the 

 teeth of fishes are slender, and so closely set together as 

 to resemble to the eye the pile of velvet, in which case they 

 are said to be en velours ;' when they are at the same 

 time extremely short and close, they are likened to smooth 

 velvet; when feeble and elongated, they are said to be 

 brushy or hair-like. Lastly, those kinds of teeth are some- 

 times so extremely small and short as to be reduced to 

 mere asperities, sensible rather to touch than sight. The 



whole are simple, and spring firom an equally simple pulpy Introduc- 

 germ. ''""■ 



In the majority of osseous fishes, besides the lips, which, 

 even when fleshy, having no peculiar muscles, can exert 

 but little strength in retaining the aliments, there is gene- 

 rally in the inside of each jaw, behind the anterior teeth, a 

 kind of membranous fold or valvule, formed by a replica- 

 tion of the interior skin, and directed backwards, of which 

 the effect is to hinder the alimentary substances, and espe- 

 cially the water gulped during respiration, from escaping 

 again by the mouth. This structure, as formerly supposed, 

 does not constitute a character restricted to the genus 

 Zeus, but exists in an infinity of fishes. The food seized 

 by the teeth of the maxillae, and detained by the valve just 

 mentioned, is carried still farther back by the teeth of the 

 palate and tongue when these exist, and is at the same 

 time prevented by the dentations of the branchial arches 

 from penetrating between the intervals of the branchiae, 

 where it might injure the delicate organs of respiration. 

 The movements of the maxillae and tongue can thus send 

 the food only in the direction of the pharynx, where it un- 

 dergoes additional action on the part of the teeth of the 

 pharyngeal bones, which triturate or carry it backwards 

 into the oesophagus. The last-named part is clothed by a 

 layer of strong, close-set, muscular fibres, sometimes form- 

 ing various bundles, the contractions of which push the 

 alimentary matter into the stomach, thus completing the 

 act of deglutition.^ 



SECT. VII. THE CIRCULATION OF FISHES. 



Fishes, in common with warm-blooded animals, are pro- 

 vided with a complete circulation for the body, and with 

 another equally complete for the organs of respiration, and 

 with a particular abdominal circulation terminating at the 

 liver by means of the vena porta ; but their peculiar cha- 

 racter consists in this, that the branchial circulation alone 

 is provided at its base with a muscular apparatus or heart, 

 corresponding to the right auricle and ventricle of the high- 

 er classes, while nothing of the kind exists at the base of 

 the circulating system of the body ; in other words, the 

 left auricle and ventricle are entirely wanting — the bran- 

 chial veins changing into arteries without any muscular en- 

 velope. 



The muscular apparatus of their circulation is composed 

 of the auricle, the ventricle, and the bvdb of the pulmonary 

 artery, and the auricle itself is preceded by a large sinus, in 

 which all the veins of the body tei-minate ; a structure 

 which gives rise to four cavities separated by restrictions, 

 into which the blood must flow in its progress from the 

 body to the branchiae. Their size is small in proportion to 

 the dimensions of the body, and does not increase in the 

 same ratio with the growth of the individual. Three of these 

 receptacles, the auricle, the heart, and the bulb, are lodged 

 in a pericardium, which is itself placed beneath the pharyn- 

 geal bones, between the inferior parts of the branchial 

 arches, and for the most part protected externally by the hu- 

 meral bones. The great venous sinus is not placed in the 

 pericardium, but between the posterior partition of that 

 cavity and the membrane which represents the diaphragm, 



' The writer of tliis treatise kept a minnow little more than half an inch long in a glass tumbler for a period of two years, during 

 which time there was no perceptible increase in its dimensions. Had it continued in its native stream, subjected to the fattening in. 

 fluence of a continuous flow of water, and a consequent increase in the quantity and variety of its natural food, its cubic dimensions 

 would probably have been twenty times greater ; yet it must have attained, prior to the lapse of a couple of years, to the usual period 

 ol' the adult state. 



- The I'rench expression of dents en vcIouts, which so frequently occurs both in the Regne Animal and the Hist. Nat. dcs Poissoni, 

 is one of the many instances, as Dr M'Murtrie has remarked, in which Baron Cuvier's expressions bid defiance to all English sy- 

 nonyms. 



» The various notices (as already intimated) of the internal stnicture of fishes contained in the article Compaeativk Anatomy of 

 this work (vol. iii.) absolve us from the propriety of presenting any details regnrding the form and constitution of the intestinal canal, 

 and of certain other important interior organs of the class. 



