[3] Origin of Species, pp. 368-9.
[4] It is, however, probable that all species of the genus retained a tiny rudiment of wings in greatly dwindled scapulo-coracoid bones. And Mr. H. O. Forbes has detected, in a recently exhumed specimen of the latter, an indication of the glenoid cavity, for the articulation of an extremely aborted humerus. (See Nature, Jan. 14th, 1892.)
[5] See especially Mr. John Wood’s papers, Proc. R. S., xiii to xvi, and xviii; also Journ. Anat., i and iii. In this connexion Darwin refers to M. Richard, Annls. d. Sc. Nat. Zoolg., tom. xviii, p. 13, 1852.
[6] Proc. Nat. Hist. Soc., Boston, 1863.
[7] Nineteenth Century, November, 1891.
[8] Descent of Man, 2nd ed., pp. 15-16.
[9] I say “probably,” because analogy points in this direction. As a matter of fact, in many cases of tissue-formation karyokinesis has not hitherto been detected. But even if in such cases it does not occur—i. e. if failure to detect its occurrence be not due merely to still remaining imperfections of our histological methods,—the large number of cases in which it has been seen to occur in the formation of sundry tissues are of themselves sufficient to indicate some important difference between cells derived from ova (metazoal), and cells which have not been so derived (protozoal). Which is the point now under discussion.
[10] Even when propagated by budding, a multicellular organism has been ultimately derived from a germ-cell.
[11] It has already been stated that both parthenogenesis and gemmation are ultimately derived from sexual reproduction. It may now be added, on the other hand, that the earlier stages of parthenogenesis have been observed to occur sporadically in all sub-kingdoms of the Metaxoa, including the Vertebrata, and even the highest class, Mammalia. These earlier stages consist in spontaneous segmentations of the ovum; so that even if a virgin has ever conceived and borne a son, and even if such a fact in the human species has been unique, still it would not betoken any breach of physiological continuity. Indeed, according to Weismann’s not improbable hypothesis touching the physiological meaning of polar bodies, such a fact need betoken nothing more than a slight disturbance of the complex machinery of ovulation, on account of which the ovum failed to eliminate from its substance an almost inconceivably minute portion of its nucleus.
[12] The spermatozooids of certain plants can be strongly attracted towards a pipette which is filled with malic acid—crowding around and into it with avidity.