TEETH. INTESTINAL TRACT. li 



as in some of the Pagelli, in many rows, as in the eel (plate cXlii), 'or be 

 deciduous with age, as in the body of the vomer among the Salruonidaa. Some 

 teeth have broad and rounded molariform crowns, as in Pagrus (plate xi), or 

 they may be laterally compressed, as in blennies, or of a lancet-shaped form, 

 as in Trichiurus ; while their cutting edge may have one, two, or three cusps, 

 and be smooth or serrated. In some fish the teeth are like bristles or 

 setiform ; or arranged so close together as to appear like pile upon velvet or 

 villiform; or mixed with rather larger ones, cardiform ; recurved, barbed 

 at their extremities ; canine like ; or compressed and cutting ; of equal or 

 unequal sizes ; and more than one form may be present in a single fish. 

 Some species have the teeth resting on a sort of basal joint or a hinge, which 

 enables them on pressure being made to be reclined towards the inside of 

 the mouth, but reverting to their original direction upon the pressure being 

 removed. The principle is not identical in all these hinged teeth, thus m 

 the angler (plate xxix) and the hake (plate lxxxv) elasticity is present solely 

 in the -substances constituting the hinge ; whereas in the pike (plate cxxvi) 

 this is not the case, but the bundles of fibres proceeding from the interior 

 of the dentine cap are elastic (0. Tomes). Fishes' teeth are constantly 

 shed and generally as constantly renewed by a second appearing from 

 beneath or else to one side. This renewal of teeth is well seen in the 

 shark, wherein a row from behind constantly fills up the one which is in 

 use. • . . 



The composition of the teeth shows many variations, but principally 

 consists of vaso dentine, which may be said to be dentinal tissue, into which 

 vascular medullary canals are prolonged, sometimes externally covered by 

 dentine which is not vascular. 



THE INTESTINAL TRACT. 



The commencement of the intestinal canal or the mouth is the common 

 receptacle of water passing to the gills for respiration, and of food transmitted 

 to the stomach for nutrition, while, as might be anticipated, its capacity is 

 large. and variously formed. But it is not my purpose to enter at present 

 on the several purposes for which the mouth is employed, or the means by 

 which these are effected, except to remark on the absence of the salivary 

 glands, which in some forms seem to be represented by mucous follicles 

 that open into the mouth below the side of the tongue, much saliva doubtless 

 being unnecessary, owing to the moist condition of their food. Also that 

 among the carp-like fish the palate is very sensitive, exceedingly vascular, 

 while from numerous small pores mucus of a solvent character exudes, 

 apparently to assist the digestion of food which the pharyngeal teeth 

 masticate. The gastric portion consists of an oesophagus and a stomach, 



d * 



