The Transactions of the Linnæan Society of London, Vol. XXII, p. 215. The estimate of Reaumur, cited by Kirby and Spence, is still higher—"in five generations one Aphis may be the progenitor of 5,904,900,000 descendants; and that it is supposed that in one year there may be twenty generations." (Introduction to Entomology, Vol. I, p. 175)
A Manual of the Anatomy of Invertebrated Animals, by T. H. Huxley, p. 206.
Respecting the Eloidea I learn that in 1879—thirty years after it had become a pest—one solitary male plant was found in a pond near Edinburgh; but "in an exhaustive inquiry on the plant made by Dr. Groenland, of Copenhagen, he could find no trace of any male specimens having been found in Europe other than the Scotch." In waters from which the Eloidea has disappeared, it seems to have done so in consequence of the growth of an Alga, which has produced turbid water unfavourable to it. That is to say, the decreased multiplication of somatic cells in some cases, is not due to any exhaustion, but is caused by the rise of enemies or adverse conditions; as happens generally with introduced species of plants and animals which multiply at first enormously, and then, without any loss of reproductive power, begin to decrease under the antagonizing influences which grow up.
A Text Book of Human Physiology. By Austin Flint, M.D., LL.D. Fourth edition. New York: D. Appleton & Co. 1888. Page 797.
This supposition I find verified by Mr. A. S. Packard in his elaborate monograph on "The Cave Fauna of North America, &c.," as also in his article published in the American Naturalist, September, 1888; for he there mentions "variations in Pseudotremia cavernarum and Tomocerus plumbeus, found living near the entrance to caves in partial daylight." The facts, as accumulated by Mr. Packard, furnished a much more complete answer to Prof. Lankester than is above given, as, for example, the "blindness of Neotoma, or the Wood-Rat of Mammoth Cave." It seems that there are also "cave beetles, with or without rudimentary eyes," and "eyeless spiders" and Myriapods. And there are insects, as some "species of Anophthalmus and Adelops, whose larvæ are lacking in all traces of eyes and optic nerves and lobes." These instances cannot be explained as sequences of an inrush of water carrying with it the remote ancestors, some of which did not find their way out; nor can others of them be explained by supposing an inrush of air, which did the like.