be aware of the facility of producing fish, by manipulation, and of 

 the enormous quantities to be so produced, I may be allowed an 

 observation or two on these points. 



Perhaps I ought, for a moment, to advert to the singular 

 assertion of Dr. Robertson, of Dunkeld — namely, that he had 

 produced trout, through the agency of the female only : — I mean, 

 by extracting the roe from the female, without subsequent 

 fecundation — that it had vivified. If this be true, previous 

 impregnation must have taken place ; which is Dr. Robertson's 

 theory. How comes it, then, that the milt of the male, and the 

 ova of the female, disappear at precisely the same time ? If 

 impregnation had occurred before the female's deposit, the male 

 would be void, or nearly so, of milt, at a period prior to such 

 deposit ; which is contradicted by the unanimous testimony of 

 numberless observations. The milt is not only a secretion of 

 gradual progress, but is imperfect, until the cavity in which it 

 forms is entirely filled. This great accumulation suddenly dis- 

 appears — completely and at once. Is it credible to suppose that 

 intromission produces this. Eminent anatomists, have, from 

 careful examinations, come to the conclusion, that, as in the case 

 of the frog, the organization of fish is such, as to render impregna- 

 tion, in utero, impossible. My own testimony must be of little 

 value ; yet from the trifling practical knowledge I possess, I 

 believe impregnation iw utero, physically impracticable. If Dr. 

 Robertson's theory be correct, it seems to me, that nature has 

 formed a superfluity in the excessive quantity of milt ; a quantity 

 easily accounted for, and necessary, on the supposition of extra 

 uterine impregnation ; the diffusion, in such an element as water, 

 requires a proportionably large amount of milt, to ensure its 

 contact with the bulk of ova. 



The artificial production of fish, is exceedingly simple. By 

 causing the spawn to flow from the female, into a vessel of water, 

 and then the milt of the male, into the same vessel ; and by im- 

 mediately stirring up the water, the ova are fecundated. That 

 fecundation has been efiectual, can be known instantly; for 

 before the milt and ova have been mixed, the latter are of a pale 



