SALMON. 27 



" Before proceeding to make additional experiments, it 

 was necessary to lay my experimental basins dry, not only for 

 the purpose of removing the young Salmon of the preceding 

 season'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 situate. Every precaution was used not only to exclude 

 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 larvse of insects abound. Pond No. 1 is 

 twenty-five feet in length by eighteen in breadth, and is fed 

 by the stream, which debouches into it at the fall. Pond 

 No. 2 is twenty-two feet in length by eighteen in breadth, 

 and is fed from pond No. 1, where the communication 

 is carefully grated with wire. Pond No. 3 is fifty feet in 

 length by thirty in breadth, and is fed by the stream, 

 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 con- 

 veyed under ground to the distance of twenty feet in a square 

 wooden pipe, grated in the same manner as the former. 

 The waste water from pond No. 3 passes down a square 

 wooden pipe two feet deep, covered at the top with wire- 

 gauze, and is conveyed under ground in a small covered 

 drain to the distance of twenty feet from the pond. The 

 water of the whole is then left to find its way to the river. 



