TEETH AND INTESTINAL TRACT. 



21 



The teeth in the salmon, 

 trout, and char are of a 

 conical shape and used more 

 for capturing than masti- 

 catiug their prey ^ they are 

 present in both upper (m) 

 and lower (ma) jaws, on the 

 vomer (u), palatine bones 

 (p), and tongue (t). They 

 are frequently shed and as 

 constantly renewed by others 



appearing from beneath or 

 else on one side of the dis- 

 carded ones. As age creeps 

 on the number of their teeth 

 become more and more 

 reduced, the teeth-bearing 

 portion of the bones dimin- 

 ish in extent more rapidly 

 in such forms as frequent 

 the sea than those which pass 

 their time in fresh waters. 



Fig. 9. Diagram of teeth inside mouth of trout : m. maxilla : 

 ma. mandible;^, palatines: t. tongue: v. vomer. 



The size and arrangement of the vomerine teeth are somewhat varied, as they 

 diminish more or less rapidly in number with certain conditions, especially the 

 character, whether saline or fresh, of the waters in which the fish live. They also vary 

 greatly in different specimens of even the same universally admitted species, from 

 what exists in the earliest period of their lives when they are in a double row, to 

 old age when all may be absent, consequently it would be unsafe to base specific 

 differences upon this dentition. When the tooth-bearing ridge commences to 

 become narrower, the teeth are at first forced into a more or less irregular single 

 line, and subsequently this ridge becomes absorbed commencing from behind and 

 gradually extending forwards and the teeth as a consequence fall out. 



The teeth in the jaws are comparatively stronger* in fresh-water trout than in 

 salmon or sea trout, as will be subsequently more fully alluded to. 



The lingual teeth or those on They are shed and renewed similarly 



the tongue are ia a row of about Jji to the other teeth in the mouth of 

 five or six on either side of the iflRl these fishes, and are more commonly 

 middle line and the largest in the loQi ™ reduced numbers or absent in 

 mouth: they are curved backwards fSffl^ naarine than in the fresh -water 

 and thus prevent the escape of ^SEi forms, 

 prey after it has been once seized. ^^ 



Fig. 10. Teeth on tongue as seen from in front. 



The mouth, situated 

 at the commencement of 

 the intestinal canal, is the 

 receptacle both of water 

 passing to the gills for re- 

 spiration and of f oodtrans- 

 mitted to the stomach 

 for nutrition. The gas- 

 tric portion of this canal 

 consists of an oesophagus 

 (cB«) and a stomach (st), 

 between which is a con- 

 striction — the cardiac — 



while at the inferior 

 extremity is a second 

 constriction termed the 

 pylorus. But due to the 

 stomach having a siphonal 

 shape, or one which some- 

 what resembles a bent 

 tube, its two orifices are 

 more or less approxi- 

 mated and cause food to 

 be retained there as in a 

 csecum. The length of 

 the intestines is shorter 



Fig. 11. 



in. small intestines 



ch, chylopoetio duct : 

 py. pyloric oseoa. 



to 75° by additions of warm water, when it became very active, and tried to leap out. In an hour 

 the temperature was increased to 80°, and after a few more minutes to 85°, when it became 

 convulsed, and, although transferred to cool water, died. When the water had sunk to 70°, a 

 smaller trout and a minnow were put in, and although the next morning the temperature had 

 sunk to 67°, the trout was dead, but the minnow had not suffered. A par of the salmon, about 

 four inches long, was similarly treated, the water in half-an-hour being raised from 60° to 70°, and 

 now it tried to escape. The water was raised to 80°, and it became torpid and convulsed j at 84° 

 it seems to have died. A char of about the same size had the water gradually raised to 80°, when 

 it appears to have succumbed. The trout tried to escape by leaping out of the water, while the 

 ohai' kept to the bottom with its head downwards, as if seeking for a cooler locality. 



* " The trout," observed Dr. J. Davy, " when it feeds principally upon fish, must be 

 extremely active and strong ; consequently, from its predatory mobile habits, acquires large teeth, 

 large fleshy fins, thick skin, and great pectoral fins for turning." 



