Essays Upon Heredity and Kindred Biological Problems

Compare on this point Nägeli in his ‘Theorie der Abstammungslehre.’ This writer also concludes from similar facts that external influences have wrought in the idioplasm, changes which were at first ineffectual, and which only increased during the course of generations up to a point at which they could produce visible changes in the plant. He does not, however, draw the further conclusion that these changes only influence the germ-plasm, for he was not aware of the distinction between germ-plasm and somatoplasm.

293

It is true that he based his opinions upon entirely erroneous theories as to the constancy of species. Compare Brock, ‘Einige ältere Autoren über die Vererbung erworbener Eigenschaften’ in ‘Biolog. Centralblatt,’ Bd. VIII, p. 491 (1888): see also Hugo Spitzer, ‘Beiträge zur Descendenz-theorie und zur Methodologie der Naturwissenschaft,’ Leipzig, 1886, pp. 515 et seq.

294

W. His, ‘Unsere Körperform,’ Leipzig, 1875.

295

See Essay II (#x9_x_9_i90) in the present volume.

296

[One of the most remarkable forms of this revival of Lamarckism is the establishment in America of a ‘Neo-Lamarckian School,’ which includes among its members many of the most distinguished American biologists. One of the arguments upon which the founders of the school have chiefly relied is derived from the comparative morphology of mammalian teeth. The evolution of the various types are believed to be due to modifications in shape, produced by the action of mechanical forces (pressure and friction) during the life of the individual. The accumulation of such modifications by means of heredity explains the forms of existing teeth.

It may be reasonably objected that the most elementary facts concerning the development of teeth prove that their shapes cannot be altered during the lifetime of the individual, except by being worn away. The shape is predetermined before the tooth has cut the gum. Hence the Neo-Lamarckian School assumes, not the transmission of acquired characters, but the transmission of characters which the parent is unable to acquire!—E. B. P.]

297

See p. 412 (#x34_x_34_i57) of the preceding Essay (VII).

298

[See ‘Nature,’ vol. xxix. p. 20, and vol. xxxv. p. 38. In the latter article nine generations are recorded, and in both articles figures of the normal and abnormal feet are given. Additional generations and many more families have been since observed, and an account of these observations will shortly be published in the same paper. The breed originally came from Bristol. In the observations recorded, the abnormality of the offspring is an indication of the hereditary strength of the female parents, while the degree of normality is a similar test of heredity through the male parents; for the female parents were always abnormal, the male parents always normal. The most abnormal kitten observed possessed seven toes on each forefoot, seven toes on the right hind foot (three more than the normal number), and six on the left hind foot. Kittens with seven toes on the forefeet and six on the hind were comparatively common, and all intermediate conditions between this and the normal were of frequent occurrence. Cats with extra toes are, I think, not uncommon in most countries, and the fact that the peculiarity is transmitted is also well known. The object of the investigation alluded to was to observe the transmission systematically through many generations.—E. B. P.]

299

Bonnet, ‘Die stummelschwänzigen Hunde im Hinblick auf die Vererbung erworbener Eigenschaften,’ Anat. Anzeiger, Bd. III, 1888, p. 584; see also ‘Beiträge zur patholog. Anatomie und allgem. Pathologie’ by Ziegler and Nauwerck, Bd. IV, 1888.

300

See the interesting remarks by Döderlein on this point, which Dr. Ischikawa of Japan tells me are quite correct. Döderlein, ‘Ueber schwanzlose Katzen,’ Zool. Anzeiger, vol. x. Nov. 1887, No. 265.

301

It is certainly true that among nations which practise circumcision as a ritual, children are sometimes born with a rudimentary prepuce, but this does not occur more frequently than in other nations in which circumcision is not performed. Rather extensive statistical investigations have led to this result.

302

See Brock, ‘Biolog. Centralblatt,’ Bd. VIII. p. 497, 1888.

303

W. Richter, ‘Zur Vererbung erworbener Charaktere,’ Biolog. Centralblatt, Bd. VIII. 1888, p. 289.

304

This case was not observed by Darwin himself, but was communicated to him by J. P. Bishop of Perry, in North America (see ‘Kosmos,’ vol. ix. p. 458). Quite apart from the fact that it is by no means certain whether the father did not already possess an innate malformation of the thumb, exact data are wanting as to the time during which the thumb was diseased, and as to the time when the malformation of the thumb was first observed in the children and the grandchildren; whether at birth or at a later period. For a thorough criticism it would also be necessary to have figures of the thumbs. I should not have alluded to this case, because of its incomplete history, if it had not appeared to me to illustrate the ideas mentioned above. Of course I do not maintain that I have suggested the right explanation in this particular case. It is possible that the father possessed an inherent malformation of the thumb which he had forgotten by the time that he came to have children and grandchildren, and was struck by the abnormality of their thumbs.

305

See Burdach, ‘Lehrbuch der Physiologie,’ Bd. II, 1835-40, p. 128.

306

See Handwörterbuch der Physiologie von Rud. Wagner, Artikel ‘Zeugung,’ von Rud. Leuckart.

307

See V. Hensen, ‘Physiologie der Zeugung.’ Leipzig, 1881.