166 Mr Shaw's Experiments on the Fry of the Salmon. 



that no doubt may exist as to their offspring being the progeny 

 of the true sahnon. I have also at stated intervals preserved 

 specimens of the young to exhibit their progress, and to vindi- 

 cate the opinion advanced in my former paper, that the salmon 

 fry do not migrate the same year they are hatched, but con- 

 tinue in the river for two years after their birth. I may at the 

 same time state, that I still adhere to my former opinion that 

 the parr is the young of the salmon, although the families of 

 the salmon in my possession have not yet reached that age when 

 their identity may be most distinctly determined. 



Before proceeding to make the experiments about to be re- 

 corded, it was necessary to lay my experimental basins dry, not 

 only for the purpose of removing the young salmon of last sea- 

 son's produce, but also to enable me to fit them up on such a 

 principle as would exclude any possibility of confusion either 

 from the overflowing of the ponds themselves, or from the 

 flooding of the river Nith, on the banks of which they are situ- 

 ated. The plan on which these ponds are constructed is shewn 

 in Plate III. Every precaution has been used not only to ex- 

 clude error, but to place the young fry in circumstances as 

 nearly resembling the state of nature as was consistent with 

 their preservation. 



The ponds, which are three in number, are two feet deep, 

 and thickly embedded with gravel, while they are at the same 

 time supplied with a small stream of spring-water in which the 

 larvae of insects abound. Pond No. 1 is 25 feet in length by 

 18 in breadth, and is fed by the stream which debouches into 

 it at the fall F. Pond No. 2 is 22 feet in length by 18 in 

 breadth, and is fed from pond No. 1 at G, where the com- 

 munication is carefully grated with wire. Pond No. 3 is 50 

 feet in length by 30 in breadth, and is fed by the stream at F, 

 having no communication with either of the other ponds. The 

 waste water from pond No. 1 is conducted into pond No. 2 

 through a square wooden pipe covered at the mouth with a wire 

 grating, the bars of which are about one-eighth of an inch apart. 

 The waste water from pond No. 2 is conveyed under ground 

 to the distance of 20 feet in a square wooden pipe grated in the 

 same manner as the former. The waste water from pond No. 3 

 passes down a squai'e wooden pipe 2 feet deep covered at the 

 top with wire-gauze, and is conveyed under ground in a sma 



