Dear Sir,

It will be a pleasure to me if I can give any aid on the subject of your letter which I received this morning.—

The exp^ts. you suggest are I think very deserving of being made & I shall be glad to make them whenever I have an opportunity, which I can hardly expect to have till next spawning season,—I allude to that of the Salmonidæ.— Even then I cannot be sure of obtaining ova: this last season I have not succeeded in getting any.

In a paper containing miscellaneous observations on the Salmonidæ lately read at a meeting of the Royal Soc^y. of Edinburgh,² I have mentioned one or two facts bearing I think on your inquiry.—³

One, the retention of life in a young Charr, (so small that might have been conveyed to a distance by a bird adhering to it’s feathers or feet), for the space of 72 hours, barely covered with water, so as to prevent it’s drying.—

Another, ova of the Salmon taken from the stomach of a trout, which proved to have been impregnated by the result, not losing their vitality; some of them, placed in water under favorable circumstances, producing young fish.—

From the exp^ts. I have already made on the ova of fish I have little doubt that those at least of the Salmonidæ, are after impregnation very retentive of life, & that mere exposure to the air, provided they be kept moist, would not kill them.— They do not appear to suffer when exposed under the microscope, using a high power,—but on the contrary their development rather seems to be accelerated.— But what would be the effect of a partial drying according to your suggestion remains to be ascertained. I suspect it would prove fatal.—

I remain, | Dear Sir | Your’s very truly | John Davy. Charles Darwin Esq^re.