Essays Upon Heredity and Kindred Biological Problems. Weismann August

chance of finding food, the larger ones less chance. That one which gave off several small portions to form each a new organism would have a better chance of leaving descendants like itself than one which divided equally or gave off a large part of itself. Hence it would happen that those which gave off very small portions would probably soon after cease to maintain their own existence while they would leave a numerous offspring. This state of things would be in any case for the advantage of the race, and would therefore, by natural selection, soon become established as the regular course of things, and thus we have the origin of old age, decay, and death; for it is evident that when one or more individuals have provided a sufficient number of successors they themselves, as consumers of nourishment in a constantly increasing degree, are an injury to those successors. Natural selection therefore weeds them out, and in many cases favours such races as die almost immediately after they have left successors. Many moths and other insects are in this condition, living only to propagate their kind and then immediately dying, some not even taking any food in the perfect and reproductive state.’—E. B. P.]

5

Johannes Müller, ‘Physiologie,’ Bd. I. p. 31, Berlin, 1840.

6

Oken, ‘Naturgeschichte,’ Stuttgart, 1837, Bd. IV. Abth. 1.

7

Brehm, ‘Leben der Vögel,’ p. 278.

8

‘Naturwissenschaftliche Thatsachen und Probleme,’ Populäre Vorträge, Berlin, 1880; vide Appendix.

9

‘Entomolog. Mag.,’ vol. i. p. 527, 1833.

10

Imhof, ‘Beiträge zur Anatomie der Perla maxima,’ Inaug. Diss., Aarau, 1881.

11

Mr. Edwards has meanwhile published these communications in full; cf. ‘On the length of life of Butterflies,’ Canadian Entomologist, 1881, p. 205.

12

When no authority is given, the observations are my own.

13

In the paper quoted above, Edwards, after weighing all the evidence, reduces the length of life from three to four weeks.

14

‘Entomolog. Mag.,’ vol. i. p. 527, 1823.

15

Ibid.

16

Ibid.

17

‘Recherches sur les mœurs des Fourmis indigènes,’ Genève, 1810.

18

These two female ants were still alive on the 25th of September following Sir John Lubbock’s letter, so that they live at least seven years. Cf. ‘Observations on Ants, Bees, and Wasps,’ Part VIII. p. 385; Linn. Soc. Journ. Zool., vol. xv. 1881.

[Sir John Lubbock has kindly given me further information upon the duration of life of these two queen ants. Since the receipt of his letter, the facts have been published in the Journal of the Linnean Society (Zoology), vol. xx. p. 133. I quote in full the passage which refers to these ants:—

‘Longevity.—It may be remembered that my nests have enabled me to keep ants under observation for long periods, and that I have identified workers of Lasius niger and Formica fusca which were at least seven years old, and two queens of Formica fusca which have lived with me ever since December 1874. One of these queens, after ailing for some days, died on the 30th July, 1887. She must then have been more than thirteen years old. I was at first afraid that the other one might be affected by the death of her companion. She lived, however, until the 8th August, 1888, when she must have been nearly fifteen years old, and is therefore by far the oldest insect on record.

‘Moreover, what is very extraordinary, she continued to lay fertile eggs. This remarkable fact is most interesting from a physiological point of view. Fertilization took place in 1874 at the latest. There has been no male in the nest since then, and, moreover, it is, I believe, well established that queen ants and queen bees are fertilized once for all. Hence the spermatozoa of 1874 must have retained their life and energy for thirteen years, a fact, I believe, unparalleled in physiology.’

‘I had another queen of Formica fusca which lived to be thirteen years old, and I have now a queen of Lasius niger which is more than nine years old, and still lays fertile eggs, which produce female ants.’

Both the above-mentioned queens may have been considerably older, for it is impossible to estimate their age at the time of capture. It is only certain (as Sir John Lubbock informs me in his letter) that they must have been at least nine months old (when captured), as the eggs of F. fusca are laid in March or early in April.’ The queens became gradually ‘somewhat lethargic and stiff in their movements (before their death), but there was no loss of any limb nor any abrasion.’ This last observation seems to indicate that queen ants may live for a much longer period in the wild state, for it is stated above that the chitin is often greatly worn, and some of the limbs lost (see pp. 48, 51, and 52).—E. B. P.]

19

A. von Berlepsch, ‘Die Biene und ihre Zucht,’ etc., 3rd ed.; Mannheim, 1872.

20

E. Bevan, ‘Ueber die Honigbiene und die Länge ihres Lebens;’ abstract in Oken’s ‘Isis,’ 1844, p. 506.

21

Dalyell, ‘Rare and Remarkable Animals of Scotland,’ vol. ii. p. 203; London, 1848.

22

[Mr. J. S. Haldane has kindly obtained details of the death of the sea anemone referred to by the author. It died, by a natural death, on August 4, 1887, after having appeared to become gradually weaker for some months previous to this date. It had lived ever since 1828 in the same small glass jar in which it was placed by Sir John Dalyell. It must have been at least 66 years old when it died.—E.B.P.]

23

Bronn, ‘Klassen und Ordnungen des Thierreichs,’ Bd. III. p. 466; Leipzig.

24

Bronn, l. c.

25

Cf. the article ‘Mort’ in the ‘Encyclop. Scienc. Méd.’ vol. M. p. 520.

26

Roux, in his work ‘Der Kampf der Theile im Organismus,’ Jena 1881, has attempted to explain the manner in which division of labour has arisen among the cells of the higher organisms, and to render intelligible the mechanical processes by which the purposeful adaptations of the organism have arisen.

27

von Berlepsch, ‘Die Biene und ihre Zucht,’ etc.

28

Oken, ‘Isis,’ 1844, p. 506.

29

von Berlepsch, l. c., p. 165.

30

Cf. August Gruber, ‘Der Theilungsvorgang bei Euglypha alveolata,’ and ‘Die Theilung der monothalamen Rhizopoden,’ Z. f. W. Z., Bd. XXXV. and XXXVI., p. 104, 1881.

31

Cf. Victor Hensen, ‘Physiologie d. Zeugung,’ p. 152.

32

Cf. J. Carrière, ‘Ueber Regeneration bei Landpulmonaten,’ Tagebl. der 52. Versammlg. deutsch. Naturf. pp. 225-226.

33

Pflüger, ‘Ueber den Einfluss der Schwerkraft auf die Theilung der Zellen und auf die Entwicklung des Embryo,’ Arch. f. Physiol. Bd. XXXII. p. 68, 1883.

34

Victor Hensen in his ‘Physiologie der Zeugung,’ Leipzig, 1881, p. 216.

35

That is for the preservation of its life.

36

Compare Weismann, ‘Die Entstehung der Sexualzellen bei den Hydromedusen,’ Jena, 1883.

37

It is doubtful whether Magosphaera should be looked upon as a mature form; but nothing hinders us from believing that species have lived, and are still living, in which the ciliated sphere has held together until the encystment, that is the reproduction, of the constituent single cells.

38

Or is an exception perhaps afforded by the nutritive cells of the egg, which occur in many animals?

39

Or more precisely, they