a single act of coition be sufficient to fecundate all the eggs existing in the ovaria at the time, how those are fecundated which did not exist there? But when we consider that in the common spider, according to Audebert, the fertilizing effect continues for _many years_; and that the fecundation of the eggs of the female aphides or green lice, by the males of one generation, will continue for a year, passing, during that period, through _nine_ or _ten successive generations_ of females, the causes for doubt will, I think, be greatly diminished: at any rate we are not at liberty to reject the evidence of facts, because we cannot understand their _modus operandi_. With respect to the aphis, Bonnet says the influence of the male continues through _five_ generations, but Lyonnet carried his experiments to a more extended period; and according to Messrs. Kirby and Spence, who give it "upon the authority of Mr. Wolnough of Hollesley (late of Boyton) in Suffolk, an intelligent agriculturist, and a most acute and accurate observer of nature, there may be _twenty_ generations in a year." Reaumur has proved that in _five_ generations one aphis may be the progenitor of 5,904,900,000 descendants. It may be objected to me here, that the aphis is a viviparous insect, and that the experiments which prove what I have referred to, do not therefore bear upon the question. It has been ascertained, however, that they are strictly oviparous at the close of the year (one species is at all times so), at other times ovo-viviparous; and in either case the penetrating influence of the male sperm is surely still more remarkable where there has been no immediate commerce with the male, than in the direct case of the oviparous bee! It has been observed, however, that the further the female aphides are removed from the first mother, or that which had known the male, the less prolific do they become. In order to put my readers in possession of Dr. Fleming's opinion upon this subject, I will quote what he has said in his Philosophy of Zoology. "Impregnation, in insects, appears to take place while the eggs pass a reservoir containing the sperm, situated near the termination of the oviduct in the vulva. In dissecting the female parts, in the silk-moth, says Mr. Hunter, I discovered a bag, lying on what may be called the vagina or common oviduct, whose mouth or opening was external, but it had a canal of communication betwixt it and the common oviduct. In dissecting these parts, before copulation, I found this bag empty; and when I dissected them afterwards, I found it full. (Phil. Trans. 1792. p. 186.) By the most decisive experiments, such as covering the ova of the unimpregnated moth, after exclusion, with the liquor taken from this bag, in those which had had sexual intercourse, and rendering them fertile, he demonstrated that this bag was a reservoir for the spermatic fluid, to impregnate the eggs, as they were ready for exclusion, and that