Chapter V: Appendix (2)

Here the replacement of the used-up elements of tissue by new ones is not taken into account, but an attempt is made to show that the functions of the whole organism necessarily cause it to waste away. But the question at once arises, whether such a result does not depend upon the fact that the single histological elements,—the cells,—are worn out by the exercise of function. Bertin admits this to be the case, and this idea of the importance of changes in the cells themselves is everywhere gaining ground. But although we must admit that the histological elements do, as a matter of fact, wear out, in multicellular animals, this would not prove that, nor explain why, such changes must follow from the nature of the cell and the vital processes which take place within it. Such an admission would merely suggest the question:—how is it that the cells in the tissues of higher animals are worn out by their function, while cells which exist in the form of free and independent organisms possess the power of living for ever? Why should not the cells of any tissue, of which the equilibrium is momentarily disturbed by metabolism, be again restored, so that the same cells continue to perform their functions for ever:—why cannot they live without their properties suffering alteration? I have not sufficiently touched upon this point in the text, and as it is obviously important it demands further consideration.

In the first place, I think we may conclude with certainty from the unending duration of unicellular organisms, that such wearing out of tissue cells is a secondary adaptation, that the death of the cell, like general death, has arisen with the complex, higher organisms. Waste does not depend upon the intrinsic nature of the cells, as the primitive organisms prove to us, but it has appeared as an adaptation of the cells to the new conditions by which they are surrounded when they come into combination, and thus form the cell-republic of the metazoan body. The replacement of cells in the tissues must be more advantageous for the functions of the whole organism than the unlimited activity of the same cells, inasmuch as the power of single cells would be much increased by this means. In certain cases, these advantages are obvious, as for example in many glands of which the secretions are made up of cast-off cells. Such cells must die and be separated from the organism, or the secretion would come to an end. In many cases, however, the facts are obscure, and await physiological investigation. But in the meantime we may draw some conclusions from the effects of growth, which are necessarily bound up with a certain rate of production of new cells. In the process of growth a certain degree of choice between the old cells which have performed their functions up to any particular time, and the new ones which have appeared between them, is as it were left to the organism.

The organism may thus, figuratively speaking, venture to demand from the various specific cells of tissues a greater amount of work than they are able to bear, during the normal length of their life, and with the normal amount of their strength. The advantages gained by the whole organism might more than compensate for the disadvantages which follow from the disappearance of single cells. The glandular secretions which are composed of cell-detritus, prove that the cells of a complex organism may acquire functions which result in the loosening of their connexion with the living cell-community of the body, and their final separation from it. And the same facts hold with the blood corpuscles, for the exercise of their function results in ultimate dissolution. Hence it is not only conceivable, but in every way probable, that many other functions in the higher organisms involve the death of the cells which perform them, not because the living cell is necessarily worn out and finally killed by the exercise of any ordinary vital process, but because the specific functions in the economy of the cell community which such cells undertake to perform, involve the death of the cells themselves. But the fact that such functions have appeared,—involving as they do the sacrifice of a great number of cells,—entirely depends upon the replacement of the old by newly formed cells, that is by the process of reproduction in cells[26].

We cannot _a priori_ dispute the possibility of the existence of tissues in which the cells are not worn out by the performance of function, but such an occurrence appears to be improbable when we recollect that the cells of all tissues owe their constitution to a very far-reaching process of division of labour, which leaves them comparatively one-sided, and involves the loss of many properties of the unicellular, self-sufficient organism. At any rate we only know of potential immortality in the cells which constitute independent unicellular organisms, and the nature of these is such that they are continually undergoing a complete process of reformation.

If we did not find any replacement of cells in the higher organism, we should be induced to look upon death itself as the direct result of the division of labour among the cells, and to conclude that the specific cells of tissues have lost, as a consequence of the one-sided development of their activities, the power of unending life, which belongs to all independent primitive cells. We should argue that they could only perform their functions for a certain time, and would then die, and with them the organism whose life is dependent upon their activity. The longer they are occupied with the performance of special functions, the less completely do they carry out the phenomena of life, and hence they lead to the appearance of retrogressive changes. But the replacement of cells is certain in many tissues (in glands, blood, etc.), so that we can never seek a satisfactory explanation in the train of reasoning indicated above, but we must assume the existence of limits to the replacement of cells. In my opinion, we can find an explanation of this in the general relations of the single individual to its species, and to the whole of the external conditions of life; and this is the explanation which I have suggested and have attempted to work out in the text.

Note 9. Death by Sudden Shock.

The most remarkable example of this kind of death known to me, is that of the male bees. It has been long known that the drone perishes while pairing, and it was usually believed that the queen bites it to death. Later observations have however shown that this is not the case, but that the male suddenly dies during copulation, and that the queen afterwards bites through the male intromittent organ, in order to free herself from the dead body. In this case death is obviously due to sudden excitement, for when the latter is artificially induced, death immediately follows. Von Berlepsch made some very interesting observations on this point, ‘If one catches a drone by the wings, during the nuptial flight, and holds it free in the air without touching any other part, the penis is protruded and the animal instantly dies, becoming motionless as though killed by a shock. The same thing happens if one gently stimulates the dorsal surface of the drone on a similar occasion. The male is in such an excited and irritable condition that the slightest muscular movement or disturbance causes the penis to be protruded[27].’ In this case death is caused by the so-called nervous shock. The humble-bees are not similarly constituted, for the male does not die after fertilizing the female, ‘but withdraws its penis and flies away.’ But the death of male bees, during pairing, must not be regarded as normal death. Experiment has shown that these insects can live for more than four months[28]. They do not, as a matter of fact, generally live so long; for—although the workers do not, as was formerly believed, kill them after the fertilization of the queen, by direct means—they prevent them from eating the honey and drive them from the hive, so that they die of hunger[29].

We must also look upon death which immediately, or very quickly, follows upon the deposition of eggs as death by sudden shock. The females of certain species of _Psychidae_, when they reproduce sexually, may remain alive for more than a week waiting for a male: after fertilization, however, they lay their eggs and die, while the parthenogenetic females of the same species lay their eggs and die immediately after leaving the cocoon; so that while the former live for many days, the latter do not last for more than twenty-four hours. ‘The parthenogenetic form of _Solenobia triquetrella_, soon after emergence, lays all her eggs together in the empty case, becomes much shrunken, and dies in a few hours.’ (Letter from Dr. Speyer, Rhoden.)

Note 10. Intermingling during the Fission of Unicellular Organisms[30].

Fission is quite symmetrical in _Amoebae_, so that it is impossible to recognise mother and daughter in the two resulting organisms. But in _Euglypha_ and allied forms the existence of a shell introduces a distinguishing mark by which it is possible to discriminate between the products of fission; so that the offspring can be differentiated from the parent. The parent organism, before division, builds the parts of the shell for the daughter form. These parts are arranged on the surface of that part of the protoplasm, external to the old shell, which will be subsequently separated as the daughter-cell. On this part the spicules are arranged and unite to form the new shell. The division of the nucleus takes place after that of the protoplasm, so that the daughter-cell is for some time without a nucleus. Although we can in this species recognise the daughter-cell for some time after separation from the parent by the greater transparency of its younger shell, it is nevertheless impossible to admit that the characteristics of the two animals are in any way different, for just before the separation of the two individuals a circulation of the protoplasm through both shells takes place after the manner described in the text, and there is therefore a complete intermingling of the substance of the two bodies.

The difference between the products is even greater after transverse fission of the _Infusoria_, for a new anus must be formed at the anterior part and a new mouth posteriorly. It is not known whether any circulation of the protoplasm takes place, as in _Euglypha_. But even if this does not occur, there is no reason for believing that the two products of division possess a different duration of life.

The process of fission in the _Diatomaceae_ seems to me to be theoretically important, because here, as in the previously-mentioned _Monothalamia_ (_Euglypha_, etc.), the new silicious skeleton is built up within the primary organism, but not, as in _Euglypha_, for the new individual only, but for both parent and daughter-cell alike[31]. If we compare the diatom shell to a box, then the two halves of the old shell would form two lids, one for each of the products of fission, while a new box is built up afresh for each of them. In this case there is an absolute equality between the products of fission, so far as the shell is concerned.

Note 11. Regeneration.

A number of experiments have been recently undertaken, in connection with a prize thesis at Würzburg, in order to test the powers of regeneration possessed by various animals. In all essential respects the results confirm the statements of the older observers, such as Spallanzani. Carrière has also proved that snails can regenerate not only their horns and eyes, but also part of the head when it has been cut off, although he has shown that Spallanzani's old statement that they can regenerate the whole head, including the nervous system, is erroneous[32].

Note 12. The Duration of Life in Plants.

The title of the work on this subject mentioned in the Text is ‘Die Lebensdauer und Vegetationsweise der Pflanzen, ihre Ursache und ihre Entwicklung,’ F. Hildebrand, Engler’s botanische Jahrbücher, Bd. II. 1. und 2. Heft, Leipzig, 1881.

Note 13.

[Many interesting facts and conclusions upon the subject of this essay will be found in a volume by Professor E. Ray Lankester, ‘On comparative Longevity in Man and the lower Animals,’ Macmillan and Co., 1870.—E. B. P.]

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Footnotes for the Appendix to Essay I.

Footnote 1:

Humboldt’s ‘Ausichten der Natur.’

Footnote 2:

This estimate is derived from observation of the time during which
these insects are to be seen upon the wing. Direct observations upon
the duration of life in this species are unknown to me.

Footnote 3:

[Sir John Lubbock has now kept a queen ant alive for nearly 15 years.
See note 2 {note 18 below} on p. 51.—E. B. P.]

Footnote 4:

[After reading these proofs Dr. A. R. Wallace kindly sent me an
unpublished note upon the production of death by means of natural
selection, written by him some time between 1865 and 1870. The note
contains some ideas on the subject, which were jotted down for
further elaboration, and were then forgotten until recalled by the
argument of this Essay. The note is of great interest in relation to
Dr. Weismann’s suggestions, and with Dr. Wallace’s permission I print
it in full below.

‘The Action of Natural Selection in Producing Old Age, Decay, and
Death.

‘Supposing organisms ever existed that had not the power of natural
reproduction, then since the absorptive surface would only increase
as the square of the dimensions while the bulk to be nourished and
renewed would increase as the cube, there must soon arrive a limit
of growth. Now if such an organism did not produce its like,
accidental destruction would put an end to the species. Any
organism therefore that, by accidental or spontaneous fission,
could become two organisms, and thus multiply itself indefinitely
without increasing in size beyond the limits most favourable for
nourishment and existence, could not be thus exterminated: since
the individual only could be accidentally destroyed,—the race would
survive. But if individuals did not die they would soon multiply
inordinately and would interfere with each other’s healthy
existence. Food would become scarce, and hence the larger
individuals would probably decompose or diminish in size. The
deficiency of nourishment would lead to parts of the organism not
being renewed; they would become fixed, and liable to more or less
slow decomposition as dead parts within a living body. The smaller
organisms would have a better 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.]

Footnote 5:

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

Footnote 6:

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

Footnote 7:

Brehm, ‘Leben der Vögel,’ p. 278.

Footnote 8:

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

Footnote 9:

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

Footnote 10:

Imhof, ‘Beiträge zur Anatomie der _Perla maxima_,’ Inaug. Diss.,
Aarau, 1881.

Footnote 11:

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

Footnote 12:

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

Footnote 13:

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

Footnote 14:

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

Footnote 15:

Ibid.

Footnote 16:

Ibid.

Footnote 17:

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

Footnote 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.]

Footnote 19:

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

Footnote 20:

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

Footnote 21:

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

Footnote 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.]

Footnote 23:

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

Footnote 24:

Bronn, l. c.

Footnote 25:

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

Footnote 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.

Footnote 27:

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

Footnote 28:

Oken, ‘Isis,’ 1844, p. 506.

Footnote 29:

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

Footnote 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.

Footnote 31:

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

Footnote 32:

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

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II.

ON HEREDITY.

1883.

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ON HEREDITY.