Essays Upon Heredity and Kindred Biological Problems. Weismann August

40

See Darwin, ‘The Variation of Animals and Plants under Domestication,’ 1875, vol. ii. chapter xxvii. pp. 349-399.

41

To this class of phenomena of course belong those acts of will which call forth the functional activity of certain groups of cells. It is quite clear that such impulses do not originate in the constitution of the tissue in question, but are due to the operation of external causes. The activity does not arise directly from any natural disposition of the germ, but is the result of accidental external impressions. A domesticated duck uses its legs in a different manner from, and more frequently than a wild duck, but such functional changes are the consequence of changed external conditions, and are not due to the constitution of the germ.

42

Upon this subject Pflüger states—‘I have made myself accurately acquainted with all facts which are supposed to prove the inheritance of acquired characters,—that is of characters which are not due to the peculiar organization of the ovum and spermatozoon from which the individual is formed, but which follow from the incidence of accidental external influences upon the organism at any time in its life. Not one of these facts can be accepted as a proof of the transmission of acquired characters.’ l. c. p. 68.

43

‘Physiologie der Zeugung.’

44

See ‘Ueber die Uebung,’ Berlin, 1881.

45

This principle was, I believe, first pointed out by Seidlitz. Compare Seidlitz, ‘Die Darwin’sche Theorie,’ Leipzig, 1875, p. 198.

46

W. Roux, ‘Der Kampf der Theile im Organismus,’ Leipzig, 1881.

47

Compare Born in ‘Zoolog. Anzeiger,’ 1883, No. 150, p. 537.

48

O. C. Marsh, ‘Odontornithes, a Monograph on the extinct toothed Birds of North America,’ Washington, 1880.

49

C. Darwin, ‘Variation of Animals and Plants under Domestication.’ Vol. I.

50

Compare ‘Der thierische Wille,’ Leipzig, 1880.

51

Steller’s interesting account of the Sea-cow (Rhytina Stelleri) proves that this suggestion is valid. This large mammal was living in great numbers in Behring Strait at the end of the last century, but has since been entirely exterminated by man. Steller, who was compelled by shipwreck to remain in the locality for a whole year, tells us that the animals were at first without any fear of man, so that they could be approached in boats and could thus be killed. After a few months however the survivors became wary, and did not allow Steller’s men to approach them, so that they were difficult to catch.—A. W., 1888.

52

Compare Schneider, ‘Der thierische Wille.’

53

[The author refers to the Academy of Arts at Munich. S. S.]

54

Compare Darwin’s ‘Descent of Man.’

55

‘Studien zur Descendenztheorie, I. Ueber den Saison-Dimorphismus der Schmetterlinge.’ Leipzig, 1875. English edition translated and edited by Professor Meldola, ‘Studies in the Theory of Descent,’ Part I.

56

The colours which have been called forth by sexual selection must also be included here.

57

Wilhelm Roux, ‘Der Kampf der Theile im Organismus.’ Leipzig, 1881.

58

Consult ‘Studien zur Descendenztheorie, IV. Über die mechanische Auffassung der Natur,’ p. 303, etc. Translated and edited by Professor Meldola; see ‘Studies in the Theory of Descent,’ p. 677, &c.

59

‘Ueber den Ursprung des Todes,’ Hamburg and Leipzig, 1883.

60

As in the case of the bodies of monks on the Great St. Bernard, or the dried-up bodies in the well-known Capuchine Monastery at Palermo.

61

Professor Gruber informs me that among the Infusoria of the harbour of Genoa, he has observed a species which encysts upon one of the free-swimming Copepoda. He has often found as many as ten cysts upon one of these Copepods, and has observed the escape of their contents whenever the water under the cover-glass began to putrefy. Here advantage is probably gained in the rapid transport of the cyst by the Crustacean.

62

The views of most biologists who have worked at this subject agree in all essentials with that expressed above. Bütschli says (Bronn’s ‘Klassen und Ordnungen des Thierreichs,’ Protozoa, p. 148): ‘The process of encystment does not appear to have originally borne any direct relation to reproduction: it appears on the contrary to have taken place originally,—as it frequently does at the present day,—either for the protection of the organism against injurious external influences, such as desiccation or the fatal effects of impure water, etc.; and also to enable the organism, after taking up an unusually abundant supply of food, to assimilate it in safety.’ Balbiani (‘Journ. de Micrographie,’ Tom. V. 1881, p. 293) says in reference to the Infusoria, ‘Un petit nombre d’espèces, au lieu de se multiplier à l’état de vie active, se reproduisent dans une sorte d’état de repos, dit état d’enkystement. Ces sortes de kystes peuvent être désignés sous le nom de kystes de reproduction, par opposition avec d’autres kystes, dans lesquels les Infusoires se renferment pour se soustraire à des conditions devenues défavorables du milieu qu’ils habitent, le manque d’air, le dessèchement, etc.—ceux-ci sont des kystes de conservation....’

63

This is of importance in so far as single individuals might be thus compelled to encyst even when the existing external conditions of life do not require it. The substance which Actinosphaerium, for example, employs in the secretion of its thick siliceous cyst must have been gradually accumulated by means of a process peculiar to the species. We can scarcely be in error if we assume that the silica accumulated in the organism cannot increase to an unlimited extent without injury to the other vital processes and that the secretion of the cyst must take place as soon as the accumulation has exceeded a certain limit. Thus we can understand that encystment may occur without any external necessity. Similarly, certain Entomostraca (e. g. Moina) produce winter-eggs in a particular generation, and these are formed even when the animals are kept in a room protected from cold and desiccation.

64

Upon this point Professor Gruber intends to publish an elaborate memoir.

65

This view has not even been proved for Actinosphaerium, upon which Götte chiefly relies. The observations which we now possess merely indicate that the animal contracts to the smallest volume possible. Compare F. E. Schulze, ‘Rhizopodenstudien,’ I, Arch. f. mikr. Anat. Bd. 10, p. 328; and Karl Brandt, ‘Ueber Actinosphaerium Eichhornii,’ Inaug. Diss.; Halle, 1877.