This last fact would at first sight seem to make against me, but we must consider that the presence of a double memory, provided it be not too conflicting, would be a part of the experience of the silk moth’s egg, which might be then as fatally puzzled by the monotony of a single memory as it would be by two memories which were not sufficiently like each other. So that failure here must be referred to the utter absence of that little internal stimulant of slightly conflicting memory which the creature has always hitherto experienced, and without which it fails to recognise itself. In either case, then, whether with hybrids or in cases of parthenogenesis, the early death of the embryo is due to inability to recollect, owing to a fault in the chain of associated ideas. All the facts here given are an excellent illustration of the principle, elsewhere insisted upon by Mr. Darwin, that _any_ great and sudden change of surroundings has a tendency to induce sterility; on which head he writes (“Plants and Animals under Domestication,” vol. ii. p. 143, ed. 1875):— “It would appear that any change in the habits of life, whatever their habits may be, if great enough, tends to affect in an inexplicable manner the powers of reproduction.” And again on the next page:— “Finally, we must conclude, limited though the conclusion is, that changed conditions of life have an especial power of acting injuriously on the reproductive system. The whole case is quite peculiar, for these organs, though not diseased, are thus rendered incapable of performing their proper functions, or perform them imperfectly.” One is inclined to doubt whether the blame may not rest with the inability on the part of the creature reproduced to recognise the new surroundings, and hence with its failing to know itself. And this seems to be in some measure supported—but not in such a manner as I can hold to be quite satisfactory—by the continuation of the passage in the “Origin of Species,” from which I have just been quoting—for Mr. Darwin goes on to say:— “Hybrids, however, are differently circumstanced before and after birth. When born, and living in a country where their parents live, they are generally placed under suitable conditions of life. But a hybrid partakes of only half of the nature and condition of its mother; it may therefore before birth, as long as it is nourished within its mother’s womb, or within the egg or seed produced by its mother, be exposed to conditions in some degree unsuitable, and consequently be liable to perish at an early period . . . ” After which, however, the conclusion arrived at is, that, “after all, the cause more probably lies in some imperfection in the original act of impregnation, causing the embryo to be imperfectly developed rather than in the conditions to which it is subsequently exposed.” A conclusion which I am not prepared to accept.