[page] 49

DARWIN'S THEORY OF PANGENESIS.

SIR,—Mr. Darwin, in his work on "Animals and Plants under Domestication," has modestly described Pangenesis as a provisional hypothesis, which might be useful until a better one should be brought forward. Some of his admirers, however, seem to forget that it is as yet only a supposition, and, by assuming it to be the true theory, tend to discourage the advancement of other hypotheses, and thus impede the progress of science. An hypothesis cannot be accepted as true, or even as probably true, merely because it appears to account for a number of phenomena; for, in many cases, and especially in this one, it is quite possible that many other hypotheses may be framed which would account for them equally well.

One of the first objections that occurs to a reader of Mr. Darwin's treatise, refers to the assumption of the existence of vast numbers of gemmules. Mr. Darwin anticipated this objection, but his explanation is very unsatisfactory. He says that a codfish produces nearly five millions of eggs, and an ascaris about sixty-four millions; and then, because these bodies are so very minute, he infers that others exist which must be infinitely smaller still—a conclusion for which I see no grounds.

It is hard to accept the assumption that an animal has, during its whole life, to keep circulating in its system, not only all the complete sets of gemmules necessary for its own development, but, in addition, sets of gemmules representing every stage of development in each of its ancestors during an indefinite number of preceding generations; but that this inconceivably vast quantity of gemmules should be contained in a microscopic germ, is a supposition which should be supported by very strong evidence to become tenable. If eggs contained those supposed multitudes of germs, comprising many similar sets for each degree of development, is it conceivable that symmetrical beings would be produced as the rule, and not monstrous masses of irregularly repeated limbs and organs?

May it not occur that gemmules required for some stage of development before maturity, would sometimes be absent? Would the animal, on arriving at that stage, and still possessing the requisite gemmules for one more advanced,, be unable to pass the missing stage, and therefore die, or continue to live without further development ?

Are any instances recorded of reversion to types entirely different from those of the parents, as might be expected if gemmules be transmitted from very remote ancestors ?

I am as yet only an admirer of Mr. Darwin's hypothesis, and would be glad to see any explanations which would make me a believer in its truth.

I remain, Sir, yours, &c,

J. D.

Cork, Nov. 13th, 1868.