SECOND DAY.] BREEDING OF FISH. 73 



by the instinct of the parent fishes, who take care to 

 deposit the impregnated eggs that are to produce 

 their offspring, only in sources continually abounding 

 in fresh and aerated water.* 



PHJS. But as every species of fish has a particular 

 and usually different time for spawning, I do not see 

 how it could be contrived to cross their breeds, or how 

 the ova of a trout, which spawns in December, could 

 be impregnated by the spermatic fluid of the grayling, 

 which spawns in May; for I conclude it would be 

 impossible to preserve the eggs of a fish out of the 

 body in a state in which they could retain or recover 

 their vitality. 



HAL. I believe I mentioned before, that I had 

 found instances, in which the ova of fish were deve- 

 loped at a different period from their natural one ; and 

 I have no doubt, that a little inquiry respecting the 

 habits of fishes would enable us to acquire a knowledge 

 of the circumstances, which either hasten or retard their 

 maturity. Plenty of food and a genial season hasten 

 the period of their reproduction, which is delayed by 



[* For success in such trials it may be well to imitate nature as closely 

 as possible, and to have the breeding box made of stone with perforated 

 stone partitions. I have heard of a failure on a large scale, made appa- 

 rently under favourable circumstances and conducted with care, in which 

 the boxes used were of wood and the partitions of perforated zinc. 

 Leeches, it is well known, can be long preserved in stone tanks, and 

 even breed in them, but not in tanks of wood. J. D.] 



