[E. Ray Lankester has suggested (Encycl. Britann., art. ‘Zoology,’ pp. 818, 819) that the blindness of cave-dwelling and deep-sea animals is also due to the fact that ‘those individuals with perfect eyes would follow the glimmer of light and eventually escape to the outer air or the shallower depths, leaving behind those with imperfect eyes to breed in the dark place. A natural selection would thus be effected.’ Such a sifting process would certainly greatly quicken the rate of degeneration due to panmixia alone.—E. B. P.] Footnote 195: Adler, ‘Zeitschrift f. wiss. Zool.,’ Bd. XXXV, 1881. Footnote 196: Compare my paper, ‘Parthenogenese bei den Ostracoden,’ in ‘Zool. Anzeiger,’ 1880, p. 82. Purely negative evidence, unless on an immense scale, is quite rightly considered to be of no great value in most cases. But the condition of these animals renders the accumulation of such evidence unusually easy, because the presence of males in a colony of Ostracodes can be proved by a very simple indirect test. Thus if a colony contains any males the _receptacula seminis_ of all mature females are filled with spermatozoa, and on the other hand we may be quite sure that males are absent, if after the examination of many mature females, no spermatozoa can be found in any of their _receptacula_. Footnote 197: We cannot, however, be absolutely certain of this, for it is conceivable that males may still occur in colonies other than those examined. Footnote 198: It has now been shown by Blochmann that males appear for a very short time towards the close of summer, as in the case of _Phylloxera_.—A. W., 1888. ------------------------------------------------------------------------ APPENDICES. Appendix I. Further considerations which oppose Nägeli’s explanation of transformation as due to internal causes[199].