84 SALMONIA. 



hasten the period of their reproduction, which 

 is delayed by want of proper nourishment, and 

 by unfavourable weather. Males and females 

 likewise, confined from each other, have their 

 generative powers impeded ; and trout, gray- 

 ling, and salmon, will not deposit their ova 

 except in running water ; so that by keeping 

 them in tanks, the period of their maturity 

 might be considerably altered. I have seen 

 char even, which had been kept in confined 

 water from September till July ; and so slow 

 had been the progress of the ova, that they ap- 

 peared to be about this time fit for exclusion, 

 though, in the natural course of things, they 

 would have been ripe in the end of October 

 of the year before. By attending to and con- 

 trolling all these circumstances, I have no 

 doubt many interesting experiments might be 

 made, as to the possibility of modifying the 

 varieties of the salmo, by impregnating the 

 ova of one species with the seminal fluid of 

 another. With fishes of other genera the task 

 would be still more easy. Carp, perch, and 

 pike, deposit their ova in still water in spring 

 and summer, when it is supplied with air by 



