46 THE NATURAL HISTORY AND HABITS 



bag shrinks in like an empty bladder, and the fish 

 dies. After the fish has been out of the egg for 

 about a fortnight, a thin skin separates from the in- 

 ward coat of the hanging belly, and then it shrinks 

 so much that it appears as entirely vanished. After 

 the belly has entirely shrunk to its proportionable 

 size, this inward skin shrinks likewise and becomes 

 the intestines ; from the mouth it forms a passage 

 into the stomach, and continues more narrowly con- 

 tracted and formed into intestines which lay one over 

 another to the outlet of the belly. It is further to 

 be observed, that the heads of the trout, when they 

 first have the heads of fishes, have not yet all the 

 usual shape or form : they look as if the snout was 

 chopped off near the eyes ; but as their bellies shrink, 

 their heads grow, the mouths are formed, and after 

 about three weeks the heads get the proper shape. 

 Lastly, I shall make a few additions which flow from 

 the former observations, and are the results of ex- 

 periments which at this present occasion I have no 

 inclination to publish. 



Section VI. 



" According to the course of nature, no trout or 

 salmon are generated in ponds or standing water. 

 They cannot be bred there if millions of pregnant eggs 

 were put into them. The young trout have for the 

 first two or three weeks a great tenacity of life ; for 

 after the head is dead, the body will live two days be* 

 fore they are quite dead : this is to be understood of 

 healthy fish kept in a current of fresh running water. 

 Although the young trout have to swim with the 

 current within the six weeks out of these breeding 

 troughs, yet they can be kept within them, six or 

 more weeks longer by particular management. They 



