Essays Upon Heredity and Kindred Biological Problems

158

Oellacher, ‘Die Veränderungen des unbefruchteten Keims des Hühncheneies. ‘Zeitschrift für wissenschaftliche Zoologie,’ Bd. XXII. p. 181. 1872.

159

Hensen, ‘Centralblatt,’ 1869, No. 26.

160

Weismann, ‘Beiträge zur Naturgeschichte der Daphnoiden,’ Leipzig, 1876-79, Abhandlung VII, and ‘Zeitschrift für wissenschaftliche Zoologie,’ Bd. XXXIII.

161

Weismann, ‘Beiträge zur Kenntniss der ersten Entwicklungsvorgänge im Insectenei,’ Bonn, 1882, p. 106.

162

W. Roux, ‘Ueber die Bedeutung der Kerntheilungsfiguren.’ Leipzig, 1883.

163

We now know that the number of loops varies considerably in different species, even when they belong to the same group of animals (e.g. Nematodes).—A.W., 1888.

164

This expression is used by bee-keepers, for instance by the well-known Baron Berlepsch. Of course, it would be more accurate to say that the queen, seeing the cell of a drone, is stimulated to lay an unfertilized egg, and that, on the other hand, she is stimulated to lay a fertilized egg when she sees the cell of a worker, or that of a queen.

165

E. Bessels, ‘Die Landois’sche Theorie widerlegt durch das Experiment.’ Zeitschrift für wissenschaftliche Zoologie, Bd. XVIII. p. 124. 1868.

166

‘Daphniden,’ Abhandlung, vi. p. 324.

167

l. c., p. 150.

168

Carl Düsing, ‘Die Regulirung des Geschlechtsverhältnisses.’ Jena. 1884.

169

I intend to publish these experiments elsewhere in connexion with other observations.

170

Weismann, ‘Daphniden,’ Abhandlung, VII. p. 329; Herbert Spencer, ‘The Principles of Biology,’ 1864, vol. i. pp. 229, 230.

171

The same fact has since been ascertained in species belonging to several groups of animal.

172

Brooks, ‘The Law of Heredity.’ Baltimore, 1883, p. 73.

173

‘Zeitschrift für wissenschaftliche Zoologie,’ Bd. XXXIII. p. 107. 1873.

174

Valaoritis, l. c., p. 6.

175

I quote from Falkenberg, in Schenk’s ‘Handbuch der Botanik,’ Bd. II. p. 219. He further states that these are the only instances hitherto known in which undoubted male cells have proved to be capable of further development when they have been unable to exercise their powers of fertilization. It must be added that the two kinds of germ-cells do not differ in appearance, but only in behaviour; the female germ-cells becoming fixed, and withdrawing one of their two flagella, while the male cells continue to swarm. But even this slight degree of differentiation requires the supposition of internal molecular differentiation.

176

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

177

‘Ueber die Berechtigung der Darwin’schen Theorie.’ Leipzig, 1868, p. 27.

178

l. c., Preface, p. vi.

179

Since the above was written many other morphological peculiarities of plants have been rightly explained as adaptations. Compare, for instance, the investigations of Stahl on the means by which plants protect themselves against the attacks of snails and slugs (Jena, 1888).—A. W., 1888.

180

l. c., pp. 117, 286.

181

Compare the second and fourth of the preceding Essays, ‘On Heredity’ and ‘The Continuity of the Germ-plasm as the Foundation of a Theory of Heredity.’

182

Compare Rauber, ‘Homo sapiens ferus oder die Zustände der Verwilderten.’ Leipzig, 1885.

183

‘Sitzungsberichte der baierischen Akademie der Wissenschaften,’ vom 18 Nov. 1865. Compare also his ‘Mechanisch-physiologische Theorie der Abstammungslehre,’ p. 102, etc.

184

Jordan, ‘Remarques sur le fait de l’existence en société des espèces végétales affines.’ Lyon, 1873.

185

S. Hermann’s ‘Handbuch der Physiologie,’ Theil II; ‘Physiologie der Zeugung,’ by V. Hensen.

186

E. van Beneden, ‘Recherches sur la maturation de l’œuf, la fécondation et la division cellulaire.’ Gand u. Leipzig, 1883, pp. 404 et seq.

187

Rolph, ‘Biologische Probleme.’ Leipzig, 1882.

188

Cienkowsky, ‘Arch. f. mikr. Anat.,’ ix. p. 47. 1873.

189

Hensen, ‘Physiologie der Zeugung,’ p. 139.

190

Coalescence takes place in the so-called bud-like conjugation of Vorticellidae and Trichodinidae, etc.

191

Compare (1) Bardeleben, ‘Zur Entwicklung der Fusswurzel,’ Sitzungsber. d. Jen. Gesellschaft, Jahrg. 1885, Feb. 6; also ‘Verhandl. d. Naturforscherversammlung zu Strassburg,’ 1885, p. 203; (2) G. Baur, ‘Zur Morphologie des Carpus und Tarsus der Wirbelthiere,’ Zool. Anzeiger, 1885, pp. 326, 486.

192

In frogs the sixth toe exists in the hind legs as a rudimentary prehallux. Compare Born, Morpholog. Jahrbuch, Bd. I, 1876.

193

I here make use of the same illustration which I employed in my first attempt to explain the effects of panmixia. Compare the second Essay ‘On Heredity.’

194

[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.]

195

Adler, ‘Zeitschrift f. wiss. Zool.,’ Bd. XXXV, 1881.

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.

197

We cannot, however, be absolutely certain of this, for it is conceivable that males may still occur in colonies other than those examined.

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.

199

Appendix to page 257.

200

l. c., p. 118.

201

l. c., p. 118.

202

Appendix to page 258.

203

l. c., p. 137.

204

Compare Brücke, ‘Farbenwechsel des Chamäleon.’ Wien. Sitzber. 1851. Also Leydig, ‘Die in Deutschland lebenden Saurier,’ 1872.

205

‘Philosophical Transactions,’ vol. cxlviii. 1858, pp. 627-644.

206

Adler, ‘Beiträge zur Naturgeschichte der Cynipiden,’ Deutsche entom. Zeitschr. XXI., 1877, p. 209; and by the same author, ‘Ueber den Generationswechsel der Eichen-Gallwespen,’ Zeitschr. f. wiss. Zool., Bd. XXXV. 1880, p. 151.

207

Beyerinck, ‘Beobachtungen über die ersten Entwicklungsphasen einiger Cynipidengallen,’ Verhandl. d. Amsterd. Akad. d. Wiss. Bd. XXII. 1883.

208

l. c., p. 144.

209

[It is now known that many such caterpillars are actually modified in colour by their surroundings, but the process appears to be indirect and secondarily acquired by the operation of natural selection, like that of the change of colour in the chamaeleon, frogs, fish, etc.; although the stimulus of light acts upon the eyes of the latter animals and upon the skin of the caterpillar. See the seventh Essay (pp. 394-397) for a more detailed account.—E. B. P.]

210

l. c., p. 150.

211

In order to make the case as simple as possible, I assume that the insectivorous bird feeds upon a single species of insect, and that the insect is only attacked by a single species of bird.

212

English Edition, translated by D’Arcy W. Thompson, B.A. London, 1883, p. 509 et seqq.

213

Appendix to page 260.

214

Ch. Darwin, ‘On the fertilization of Orchids by Insects.’ London, 1877.

215

Compare Hermann Müller, ‘Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen beider.’ Leipzig, 1873. See also many articles by the same author in ‘Kosmos,’ and other periodicals. These later articles are included in the English translation by D’Arcy W. Thompson.

216

‘Lectures on the Physiology of Plants,’ translated by H. Marshall Ward, Oxford, 1887, p. 47.

217

Appendix to page 267.

218

Brown-Séquard, ‘Researches on epilepsy; its artificial production in animals and its etiology, nature, and treatment.’ Boston, 1857. Also various papers by the same author in ‘Journal de physiologie de l’homme,’ Tome I and III, 1858, 1860, and in ‘Archives de physiologie normale et pathologique,’ Tome I-IV, 1868-1872.

219

‘Oesterreichische medicinische Jahrbücher.’ Jahrgang, 1875, p. 179.

220

A direct transmission of the germs of disease through the reproductive cells has lately been rendered probable in the case of tuberculosis, for the bacilli have been found in tubercles in the lungs of an eight-months’ fœtal calf, the mother being affected at the time with acute tuberculosis. However it is not impossible that infection may have arisen through the placenta. See ‘Fortschritte der Medicin,’ Bd. III, 1885, p. 198.

221

Compare Unvericht, ‘Experimentelle und klinische Untersuchungen über die Epilepsie.’ Berlin, 1883. With regard to the question of hereditary transmission, the part of the brain in which the epileptic centre is placed is of no importance.

222

Compare Ziemssen’s Handbuch der spec. Pathologie und Therapie.’ Bd. XII. 2. Hälfte; Artikel ‘Epilepsie und Eklampsie.’ Leipzig, 1877.

223

l. c., p. 269.

224

It is generally known that the earlier physiologists believed in what was called the ‘evolutionary theory,’ or the ‘theory of preformation.’ This assumes that the germ contains, in a minute form, the whole of the fully-developed animal. All the parts of the adult are preformed in the germ, and development only consists in the growth of these parts and their more perfect arrangement. This theory was generally accepted until the middle of the last century, when Kaspar Friedrich Wolff brought forward the theory of ‘epigenesis,’ which since that time has been the dominant one. This assumes that no special parts of the germ are preformations of certain parts of the fully-developed animal, and that these latter arise by a series of changes in the germ, which gradually gives rise to them. In modern times the theory of preformation has been revived in a less crude form, as is shown by the ideas of Nägeli, and by Darwin’s ‘pangenesis.’—A. W., 1888.

225

Nägeli, l. c. p. 110.

226

See Darwin, ‘The Variation of Animals and Plants under Domestication.’ 1875. Vol. I. p. 311.

227

Appendix to page 290.

228

Weismann, ‘Naturgeschichte der Daphnoiden,’ Zeitschrift f. wiss. Zool. XXIII. 1879.

229

Appendix to page 277.

230

Compare W. K. Brooks, ‘The Law of Heredity, a Study of the Cause of Variation, and the Origin of living Organisms.’ Baltimore, 1883.

231

l. c., p. 82.

232

This seems to be the general opinion (see the quotation from Huxley in Brooks’ ‘Heredity,’ p. 127); but I rather doubt whether there is such a constant difference between mules and hinnies. Furthermore, I cannot accept the opinion that mules always resemble the ass more than the horse. I have seen many mules which bore a much stronger likeness to the latter. I believe that it is at present impossible to decide whether there is a constant difference between mules and hinnies, because the latter are very rarely seen, and because mules are extremely variable. I attempted to decide the question last winter by a careful study of the Italian mules, but I could not come across a single hinny. These hybrids are very rarely produced, because it is believed that they are extremely obstinate and bad-tempered. I afterwards saw two true hinnies at Professor Kühn’s Agricultural Institute at Halle. These hinnies by no means answered to the popular opinion, for they were quite tractable and good-tempered. They looked rather more like horses than asses, although they resembled the latter in size. In this case it was quite certain that one parent was a stallion and the other a female ass.—A. W. 1889.

233

Darwin, ‘Variation of Animals and Plants under Domestication,’ 1875, Vol. II. p. 41.

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.

259

See p. 364.

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.

275

See the second Essay.

276

Consult ‘Ueber die Vererbung,’ Jena, 1883; ‘Die Kontinuität des Keimplasmas,’ Jena, 1885; ‘Ueber die Zahl der Richtungskörper und über ihre Bedeutung für die Vererbung,’ Jena, 1887. These papers are translated as the second, fourth and sixth Essays in the present volume.