Footnotes for Essay VI.
[234]. See Berichten der Naturforschenden Gesellschaft zu Freiburg i. B., Band III. (1887) Heft I, ‘Ueber die Bildung der Richtungskörper bei thierischen Eiern,’ by August Weismann and C. Ischikawa.
[235]. Vol. I. p. 60.
[236]. The most recent example of this kind is afforded by the excellent work of O. Schultze, ‘Ueber die Reifung und Befruchtung des Amphibieneies,’ Zeitschr. f. wiss. Zool., Bd. XLV. 1887. Schultze has proved that two polar bodies are expelled from the egg of the Axolotl and of the frog, although all previous observers, including O. Hertwig, had been unable to find them. Thus the latter authority states as the result of an investigation specially directed towards this point, that the nucleus is transformed in a peculiar manner (‘Befruchtung des thierischen Eies,’ III. p. 81).
[237]. O. Hertwig, ‘Beiträge zur Kenntniss der Bildung, Befruchtung, und Theilung des thierischen Eies,’ Morpholog. Jahrbuch, I, II, and III. 1875-77.
[238]. H. Fol, ‘Recherches sur la fécondation et le commencement de l’hénogénie chez divers animaux.’ Genève, Bâle, Lyon, 1879.
[239]. Bütschli, ‘Entwicklungsgeschichtliche Beiträge,’ Zeitschr. f. wiss. Zool. Bd. XXIX. p. 237. 1877.
[240]. C. S. Minot, ‘Account, etc.’ Proceedings Boston Soc. Nat. Hist., vol. xix. p. 165. 1877.
[241]. F. M. Balfour, ‘Comparative Embryology.’
[242]. Nägeli, ‘Mechanisch-physiologische Theorie der Abstammungslehre,’ München und Leipzig, 1884.
[243]. See the [second] and [fourth] Essays in the present volume.
[244]. Hensen, ‘Die Grundlagen der Vererbung,’ Zeitschr. f. wiss. Landwirthschaft. Berlin, 1885, p. 749.
[245]. O. Hertwig, ‘Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbelthiere.’ Jena, 1886.
[246]. Bütschli, ‘Gedanken über die morphologische Bedeutung der sog. Richtungskörperchen,’ Biol. Centralblatt, Bd. VI. p. 5. 1884.
[247]. This observation was first published as a note at the end of the fourth Essay in the present volume. See p. [249].
[248]. Weismann, ‘Richtungskörper bei parthenogenetischen Eieren,’ Zool. Anzeiger, 1886, p. 570.
[249]. Blochmann, ‘Ueber die Richtungskörper bei den Insekteneiern,’ Biolog. Centralblatt., April 15, 1887.
[250]. F. Stuhlmann, ‘Die Reifung des Arthropodeneies nach Beobachtungen an Insekten, Spinnen, Myriapoden und Peripatus,’ Berichte der naturforschenden Gesellschaft zu Freiburg i. Br., Bd. I. p. 101.
[251]. In the summer-eggs of Rotifera I have, together with Mr. Ischikawa, observed one polar body, and we were able to establish for certain that a second is not formed. The nuclear spindle had already been observed by Tessin, and Billet had noticed polar bodies in Philodina, but without attaching any importance to their number. These latter observations were not conclusive proofs of the formation of polar bodies in parthenogenetic eggs, so long as it was not known whether the summer-eggs of Rotifera may develope parthenogenetically, or whether they can only develope in this way. Knowing now that parthenogenetic eggs expel only one polar body, we may perhaps be permitted to draw the conclusion that the summer-egg of a Rotifer (Lacinularia) which expelled only one polar body must have been a parthenogenetic egg. But I may add that we have also succeeded in directly proving the occurrence of parthenogenesis in Rotifera, as will be described in detail in another paper.
[252]. See Essay IV, Part III. p. [225].
[253]. E. Bessels, ‘Die Landois’sche Theorie, widerlegt durch das Experiment.’ Zeitschr. f. wiss. Zool. Bd. XVIII. p. 124. 1868.
[254]. l. c., p. 110.
[255]. Strasburger, ‘Neue Untersuchungen über den Befruchtungsvorgang bei den Phanerogamen als Grundlage einer Theorie der Zeugung.’ Jena, 1884.
[256]. Wilhelm Roux, ‘Ueber die Bedeutung der Kerntheilungsfiguren.’ Leipzig, 1884.
[257]. E. van Beneden, ‘Recherches sur la maturation de l’œuf, la fécondation et la division cellulaire.’ Gand et Leipzig, Paris, 1883.
[258]. J. B. Carnoy, ‘La Cytodiérèse de l’œuf, la vésicule germinative et les globules polaires de l’Ascaris megalocephala.’ Louvain, Gand, Lierre, 1886.
[260]. Wilhelm Roux, ‘Beiträge zur Entwicklungsmechanik des Embryo,’ No. 3, Breslauer ärztliche Zeitschrift, 1885, p. 45.
[261]. Carnoy, ‘La Cytodiérèse chez les Arthropodes.’ Louvain, Gand, Lierre, 1885.
[262]. Flemming, ‘Neue Beiträge zur Kenntniss der Zelle.’ Arch. f. mikr. Anat. Bd. XXIX, 1887.
[263]. Carnoy, ‘La Cytodiérèse de l’œuf; la vésicule germinative et les globules polaires chez quelques Nématodes.’ Louvain, Gand, Lierre. 1886.
[264]. Hensen, ‘Die Grundlagen der Vererbung nach dem gegenwärtigen Wissenskreis,’ Zeitschr. f. wissenschaftl. Landwirthschaft, Berlin, 1885, p. 731.
[265]. See the preceding [Essay] on ‘The Significance of Sexual Reproduction in the theory of Natural Selection.’
[266]. E. van Beneden and Julin, ‘La Spermatogénèse chez l’Ascaride mégalocéphale.’ Brussels, 1884.
[267]. Carnoy, ‘La Cytodiérèse chez les Arthropodes.’
[268]. Gustav Platner, ‘Die Karyokinese bei den Lepidopteren als Grundlage für eine Theorie der Zelltheilung.’ Internation. Monatsschrift f. Anatomie und Histologie, Bd. III. Heft 10. Leipzig, 1886.
[269]. La Valette St. George, ‘Ueber die Genese der Samenkörper.’ Fünfte Mittheilung. Die Spermatogenese bei den Säugethieren und dem Menschen,’ Archiv f. mikrosk. Anat. Bd. XV. 1878.
[270]. Weismann, ‘Studien zur Descendenztheorie,’ ii. p. 306, Leipzig, 1876, translated by Meldola; see ‘Studies in the Theory of Descent,’ p. 680.
[271]. l. c., p. 92.
[272]. [The similar conclusion that identical ova lead to the appearance of identical individuals was drawn from the same data by Francis Galton in 1875. See ‘The history of the Twins, as a criterion of the relative powers of Nature and Nurture,’ by Francis Galton, F.R.S., Journal of the Anthropological Institute, 1875, p. 391; also by the same author, ‘Short Notes on Heredity, etc. in Twins,’ in the same Journal, 1875, p. 325.
The author investigated about eighty cases of close similarity between twins, and was able to obtain instructive details in thirty-five of these. Of the latter there were no less than seven cases ‘in which both twins suffered from some special ailment or had some exceptional peculiarity;’ in nine cases it appeared that ‘both twins are apt to sicken at the same time;’ in eleven cases there was evidence for a remarkable association of ideas; in sixteen cases the tastes and dispositions were described as closely similar. These points of identity are given in addition to the more superficial indications presented by the failure of strangers or even parents to distinguish between the twins. A very interesting part of the investigation was concerned with the after-lives of the thirty-five twins. ‘In some cases the resemblance of body and mind had continued unaltered up to old age, notwithstanding very different conditions of life,’ in the other cases ‘the parents ascribed such dissimilarity as there was, wholly, or almost wholly, to some form of illness.’
The conclusions of the author are as follows: ‘Twins who closely resembled each other in childhood and early youth, and were reared under not very dissimilar conditions, either grow unlike through the development of natural characteristics which had lain dormant at first, or else they continue their lives, keeping time like two watches, hardly to be thrown out of accord except by some physical jar. Nature is far stronger than nurture within the limited range that I have been careful to assign to the latter.’ And again, ‘where the maladies of twins are continually alike, the clocks of their two lives move regularly on, and at the same rate, governed by their internal mechanism. Necessitarians may derive new arguments from the life histories of twins.’
The above facts and conclusions held for twins of the same sex, of which at any rate the majority are shown by Kleinwächter’s observations to have been enclosed in the same embryonic membranes, and therefore presumably to have been derived from a single ovum; but in rarer cases the twins, although also invariably of the same sex, were marked by remarkable differences, greater than those which usually distinguish children of the same family. Mr. Galton met with twenty of these cases. In such twins the conditions of training, etc. had been as similar as possible, so that the evidence of the power of nature over nurture is strongly confirmed. Mr. Galton writes, ‘I have not a single case in which my correspondents speak of originally dissimilar characters having become assimilated through identity of nurture. The impression that all this evidence leaves on the mind is one of wonder whether nurture can do anything at all, beyond giving instruction and professional training.’
The fact that twins produced from a single ovum seem to be invariably of the same sex is in itself extremely interesting, for it proves that the sex of the individual is predetermined in the fertilized ovum.—E. B. P.]
[273]. Fol, Recherches sur la fécondation et le commencement de l’hénogénie: Genève, Bâle, Lyon. 1879.
[274]. Born, ‘Ueber Doppelbildungen beim Frosch und deren Entstehung.’ Breslauer ärztl. Zeitschrift, 1882.
VII.
ON THE SUPPOSED BOTANICAL PROOFS
OF THE
TRANSMISSION OF ACQUIRED CHARACTERS.
1888.
From ‘Biologisches Centralblatt,’ Bd. VIII. Nr. 3 and 4, pages 65
and 97: April 1888.