Essays Upon Heredity and Kindred Biological Problems

Professor Meldola points out to me that Darwin did not admit that Galton’s experiments disproved pangenesis (‘Nature,’ April 27, 1871, p. 502), and Galton also admitted this in the next number of ‘Nature’ (May 4, 1871, p. 5).—A. W. 1889.

99

Weismann, ‘Ueber die Vererbung.’ Jena, 1883; translated in the present volume as the second essay ‘On Heredity.’

100

E. Roth, ‘Die Thatsachen der Vererbung.’ 2. Aufl., Berlin, 1885, p. 14.

101

Jäger, ‘Lehrbuch der allgemeinen Zoologie,’ Bd. II. Leipzig, 1878.

102

M. Nussbaum, ‘Die Differenzirung des Geschlechts im Thierreich,’ Arch. f. Mikrosk. Anat., Bd. XVIII. 1880.

103

I have since learnt that Professor Rauber of Dorpat also expressed similar views in 1880; and Professor Herdman of Liverpool informs me that Mr. Francis Galton had brought forward in 1876 a theory of heredity of which the fundamental idea in some ways approached that of the continuity of the germ-plasm (‘Journal of the Anthropological Institute,’ vol. v; London, 1876).—A. W., 1888.

[A less complete theory was brought forward by Galton at an earlier date, in 1872 (see Proc. Roy. Soc. No. 136, p. 394). In this paper he proposed the idea that heredity chiefly depends upon the development of the offspring from elements directly derived from the fertilized ovum which had produced the parent. Galton speaks of the fact that ‘each individual may properly be conceived as consisting of two parts, one of which is latent and only known to us by its effects on his posterity, while the other is patent, and constitutes the person manifest to our senses. The adjacent and, in a broad sense, separate lines of growth in which the patent and latent elements are situated, diverge from a common group and converge to a common contribution, because they were both evolved out of elements contained in a structureless ovum, and they, jointly, contribute the elements which form the structureless ova of their offspring.’ The following diagram shows clearly ‘that the span of each of the links in the general chain of heredity extends from one structureless stage to another, and not from person to person:—

Structureless elements {…Adult Father… } structureless elements

in Father         {…Latent in Father…} in Offspring.’

Again Galton states—‘Out of the structureless ovum the embryonic elements are taken … and these are developed (a) into the visible adult individual; on the other hand …, after the embryonic elements have been segregated, the large residue is developed (b) into the latent elements contained in the adult individual.’ The above quoted sentences and diagram indicate that Galton does not derive the whole of the hereditary tendencies from the latent elements, but that he believes some effect is also produced by the patent elements. When however he contrasts the relative power of these two influences, he attaches comparatively little importance to the patent elements. Thus if any character be fixed upon, Galton states that it ‘may be conceived (1) as purely personal, without the concurrence of any latent equivalents, (2) as personal but conjoined with latent equivalents, and (3) as existent wholly in a latent form.’ He argues that the hereditary power in the first case is exceedingly feeble, because ‘the effects of the use and disuse of limbs, and those of habit, are transmitted to posterity in only a very slight degree.’ He also argues that many instances of the supposed transmission of personal characters are really due to latent equivalents. ‘The personal manifestation is, on the average, though it need not be so in every case, a certain proof of the existence of latent elements.’ Having argued that the strength of the latter in heredity is further supported by the facts of reversion, Galton considers it is safe to conclude ‘that the contribution from the patent elements is very much less than from the latent ones.’ In the later development of his theory, Galton adheres to the conception of ‘gemmules’ and accepts Darwin’s views, although ‘with considerable modification.’ Together with pangenesis itself, Galton’s theory must be looked upon as preformational, and so far it is in opposition to Weismann’s theory which is epigenetic. See Appendix IV. to the next Essay (V.), pp. 316-319.—E. B. P.]

104

Nägeli, ‘Mechanisch-physiologische Theorie der Abstammungslehre.’ München u. Leipzig, 1884.

105

O. Hertwig, ‘Beiträge zur Kenntniss der Bildung, Befruchtung und Theilung des thierischen Eies.’ Leipzig, 1876.

106

Fol, ‘Recherches sur la fécondation, etc.’ Genève, 1879.

107

Kölliker formerly stated, and has again repeated in his most recent publication, that the spermatozoa (‘Samenfäden’) are mere nuclei. At the same time he recognizes the existence of sperm-cells in certain species. But proofs of the former assertion ought to be much stronger in order to be sufficient to support so improbable a hypothesis as that the elements of fertilization may possess a varying morphological value. Compare Zeitschr. f. wiss. Zool., Bd. XLII.

108

F. M. Balfour, ‘Comparative Embryology,’ vol. i. p. 69.

109

Arch. f. mikr. Anat., Bd. 23. p. 182, 1884.

110

Born, ‘Biologische Untersuchungen,’ I, Arch. Mikr. Anat., Bd. XXIV.

111

Roux, ‘Beiträge zum Entwicklungsmechanismus des Embryo,’ 1884.

112

O. Hertwig, ‘Welchen Einfluss übt die Schwerkraft,’ etc. Jena, 1884.

113

[Our present knowledge of the development of vegetable ova (including the position of the parts of the embryo) is also in favour of the view that it is not influenced by external causes, such as gravitation and light. It takes place in a manner characteristic of the genus or species, and essentially depends on other causes which are fixed by heredity, see Heinricher ‘Beeinflusst das Licht die Organanlage am Farnembryo?’ in Mittheilungen aus dem Botanischen Institute zu Graz, II. Jena, 1888.—S. S.]

114

E. van Beneden, ‘Recherches sur la maturation de l’œuf,’ etc., 1883.

115

M. Nussbaum, ‘Ueber die Veränderung der Geschlechtsprodukte bis zur Eifurchung,’ Arch. Mikr. Anat., 1884.

116

Eduard Strasburger, ‘Neue Untersuchungen über den Befruchtungsvorgang bei den Phanerogamen als Grundlage für eine Theorie der Zeugung.’ Jena, 1884.

[It is now generally admitted that, in the Vascular Cryptogams, as also in Mosses and Liverworts, the bodies of the spermatozoids are formed by the nuclei of the cells from which they arise. Only the cilia which they possess, and which obviously merely serve as locomotive organs, are said to arise from the surrounding cytoplasm. It is therefore in these plants also the nucleus of the male cell which effects the fertilization of the ovum. See Göbel, ‘Outlines of Classification and Special Morphology,’ translated by H. E. F. Garnsey, edited by I. B. Balfour, Oxford, 1887, p. 203, and Douglas H. Campbell, ‘Zur Entwicklungsgeschichte der Spermatozoiden,’ in Berichte d. deutschen bot. Gesellschaft, vol. v (1887), p. 120.—S. S.]

117

O. Hertwig, ‘Das Problem der Befruchtung und der Isotropie des Eies.’ Jena, 1885.

118

This opinion was first expressed in my lecture, ‘Ueber die Dauer des Lebens,’ Jena, 1882, translated as the first essay in the present volume.

119

M. Nussbaum, ‘Sitzungber. der Niederrheinischen Gesellschaft fur Natur- und Heilkunde.’ Dec. 15, 1884.

120

A. Gruber, ‘Biologisches Centralblatt,’ Bd. IV. No. 23, and V. No. 5.