676 



ICHTHYOLOGY. 



Structure cupies an oblique position. When the mouth is open- 



n(i . ed, it is in general of an oblong or oval shape. In some 



F f u j) "{J [ s fishes, its capacity is less than the size of the head ; 



- ' _j j but, in general, it is capable of opening to a great width, 

 sometimes superior to the thickness of the body. 



Lips. 1 ne I'P* f fi^es are seldom regularly formed. In 



a few species, however, these surround the mouth, and 

 are of a firm, fleshy consistence. In other instances, 

 the lips are of an osseous texture, divided into plates 

 which fold over one another. Such kind of lips give 

 to the mouth increased dimensions, as they are capable 

 of being exserted or folded up at the pleasure of the 

 animal. 



jtwt. Thejatvs are moveable, and both are attached to the 



bones of the palate. They are seldom equal, the one 

 exceeding the other in length. They furnish, by their 

 position and mode of union, many important characters 

 in the classification of fishes. These characters have 

 been lately investigated by Cuvier with his usual suc- 

 cess ; and he is of opinion, that the maxillary and in- 

 termaxillary bones will furnish characters not for gene- 

 ra merely, but likewise for orders. 



Teeth. The teeth of fishes exhibit remarkable differences, 



with regard to number, situation, and structure. In 

 the higher orders of animals, the number of teeth in 

 the mouth is almost always constant in the same gene- 

 ra and species. But among fish, the teeth are often so 

 numerous that it is difficult to count them, especially 

 as they occupy so many different positions. The jaws 

 are not exclusively employed to support these organs, 

 as in quadrupeds ; the tongue, the palate, the throat, 

 being often furnished with them. In the saw-fish, the 

 teeth are inserted on each side of its flattened and pro- 

 jecting snout. In the genus Sparus, the front teeth re- 

 semble those of the human species. They are provided 

 with fangs, which are contained in alveoli. In many 

 fishes, the teeth are formed of processes of the jaw 

 bones covered with enamel. Those of the shark tribe 

 adhere merely to the gums, or at least to a firm cartila- 

 ginous substance which covers the jaw. They are not 

 formed, as in the mammalia, by the addition of new 

 layers, one within the other, but apparently in a man- 

 ner resembling the formation of bone. They are at 

 first soft and cartilaginous, and pass, by successive gra- 

 dations, into a state of hardness and density not inferior 

 to that of ivory. In the skate, the teeth consist of an 

 assemblage of tubes, covered externally by enamel, and 

 connected to the jaw by a softer substance, which pro- 

 bably sends processes or vessels into those bony tubes. 



The teeth of fishes are in general bent inwards, to 

 enable them to retain their prey. As few fishes masti- 

 cate, they have seldom any teeth which resemble grind- 

 ers, although those which live on the harder shell-fish 

 have teeth fitted for triturating these. 



In the classification of fishes, the teeth furnish seve- 

 ral important characters, which are little liable to vari- 

 ation. In the genus Squalus, in particular, the teeth 

 exhibit many remarkable differences in form, sufficient, 

 in the absence of other characters, for the discrimina- 

 tion of the species. 



Gullet The gullet or oesophagus, on account of the absence 



of a neck, is in fishes remarkably short. In some, in- 

 deed, the stomach seems to open directly into the 

 mouth. Where it exists, it exhibits few peculiarities 

 of structure. In some of the branchiostegi it is beset 

 with tufts of hair resembling a fine net-work. It is in 

 general capable of great dilation, and when the sto- 

 mach is unable to hold the whole of the prey which 



has been seized, a part remains in the gullet until the Structure 

 inferior portion gives way. am ' 



The stomach of fishes is in general thin and membra- " pish 

 naceous, differing little in its structure and appearance v__ "* ^ 

 from the gullet. It frequently contains the remains of stomacU. 

 crustaceous animals, still retaining their form, but great- 

 ly altered in consistency. Hence naturalists have con. 

 eluded, that the food is reduced by solution, and not by 

 trituration. But in some fishes, particularly those which 

 subsist principally on shell-fish, the stomach has thick 

 muscular coats. Its shape is considerably different in 

 the different species, but the characters furnished by this 

 organ are seldom regarded. 



The intestines exhibit many remarkable peculiarities, intestines, 

 Sometimes they proceed directly from the stomach to 

 the anus in nearly a straight line. In other instances, 

 they form in their course one or more flexures. In some 

 instances, the gut is widest towards the stomach, and 

 gradually becomes smaller as it approaches the anus, 

 while in others the reverse of this is the case. It is 

 furnished internally in some species with spiral valves, 

 in others with lozen-shaped hollows, while in a few it 

 has numerous fringed laminae. Between the great and 

 small intestines, in the chondropterygii, there is a kind 

 of cfficum or appendix vermiformis ; but in osseous 

 fishes, there is no appearance of any such organ. In 

 the last division, however, there are bodies which have 

 been termed Appendices, or Intestinula-cceca. These 

 are situated at the origin of the gut, in a double or sin- 

 gle row. They vary in number, shape, or size, accord- 

 ing to the species ; but continue the same in all the in- 

 dividuals of the same species. In place of these in the 

 chondropterygii, there is a glandular body, which has 

 been compared to the pancreas of warm-blooded ani. 

 mals. The character for the discrimination of the spe- 

 cies furnished by the appendages is of importance, as 

 being easily investigated and permanent. 



These intestines, and the rest of the viscera situated 

 in the cavity of the abdomen, are contained in a mem- 

 branaceous sac or peritoneum. This is silvery in some 

 fishes, black or spotted in others. We are informed 

 by Willoughby, that this sac opens externally near the 

 anus by means of two small holes. These openings 

 were afterwards examined by Monro, who found in 

 each of these passages a semilunar membrane or valve, 

 so placed as to allow liquors to get out from the abdo- 

 men readily, but to resist somewhat their entry into it. 



The anus in fishes, occupies many different positions 

 according to the species. This circumstance was seiz- 

 ed upon by Scopoli, in the system which we have no- 

 ticed above, and was raised to the dignity of a primary 

 character in his system. This orifice is not merely the 

 opening whence issue the faeces, but in general the 

 spawn also. 



SECT. IX. Organs of Absorption. 



THE vessels of the absorbent system of fishes are ana- Organs of 

 logous to those of quadrupeds. They are, however, des- absorption. 

 titute of valves, unless at their termination in the red 

 veins, and do not appear to possess conglobate glands. 

 Dr Monro, to whom we are indebted for the first illus- 

 tration of this class of vessels, gives the following view 

 of their arrangement in the cod and the salmon. " The 

 chief branches," he says, " of the lacteal vessels of the 

 great and small intestines, and which are smaller in 

 proportion to the blood vessels than in the nantes pin- 

 nati of Linnaeus, run upwards in the mesentery, almost 



