SALMONID^. 59 



it is said, tlicreby a release from certain parasitical animals, gene- 

 rated, these by the fresh, those by the salt water, at each change of 

 waters. 



In Great Britain, the period of the Salmon's spawning varies from 

 November to the end of January. They have been carefully watched 

 during the whole process, as have the eggs after their deposition, so 

 that the length of time which it takes them to attain to maturity is 

 accurately known. This time has been ascertained by Mr. Shaw, in 

 a series of experiments, of which I shall have occasion to speak more 

 fully hereafter, to be about 



114 days, when the temperature of the water is - - 36° 

 101 days, ----_. 430 



90 days, -_.___ 45° 



These experiments were performed in the open air, and in natural 

 streams, liable to the ordinary influences of the atmosphere and 

 weather. 



Dr. Knox, however, as is recorded in the Transactions of the Royal 

 Society of Edinburgh, observed a pair of Salmon which completed 

 their spawning, and covered up their ova with gravel, in the usual 

 way, on the 2d of November. This was in one of the northern tribu- 

 taries of the Tweed. 



On the 25th of February, or at the end of one hundred and sixteen 

 days, the ova were dug up, and found unchanged. On being removed, 

 however, at this stage, and placed in bottles of water in warm rooms, 

 the eggs were matured almost immediately, and the young fry hatched. 

 In this state they can be preserved in the bottles, with the water un- 

 changed, for about ten days, as during that time they are suppoi'ted 

 on the yolk of the egg which adheres to the under part of their bodies, 

 as exhibited in figure 1 on the cut at the head of this article. 



On the 23d of March, according to Dr. Knox, the ova began to 

 change, and it was not until the 1st of April that the fry were found 

 to have quitted the beds. 



Mr. Shaw's experiments were, however, so conducted as to furnish 

 data on which more reliance may be placed ; and as these are of the 

 greatest interest, and as from experiments similarly conducted, farther 

 results of a different kind might be attained, of surpassing importance, 

 I shall state them somewhat at length. 



