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Phenomena,' Mr. Leo H. Grindon has discussed what he terms the various leases of life in plants and animals, using, the data and inferences of Bacon, Hufeland, and Flourens to a very large extent, but adding some which are of value. The relation of length of life to bulk, intensity, and fertility, which have been more or less clearly apparent to all who have thought on the matter from early times, are briefly set forth, and apparent exceptions to the laws enunciated are attributed to special design on the part of the Creator, to serve the special requirements of the exceptional organism, or of some other organism dependent on it.

Lastly, in regard to works, the volumes of Mr. Herbert Spencer must be mentioned. For whether we accept the new philosophy of Evolution, so marvellously born of Mr. Darwin's theory of the Origin of Species, or cling to an older belief, the fitness. of things to their conditions, the correspondences of organisms to their environment, so ably set forth in Mr. Spencer's grand work, must enter into our theory of Nature. It may be a fair boast of the evolutionist that the founder of his philosophy has been led by the course of his speculations to trace a closer connection, a more complete adaptation of living things to their wants than the teleologist ever even hinted at, much as such a close connection would have added to the consistency of his theory of design. In his 'Principles of Biology,' Mr. Spencer, in the

chapters on Genesis and on Multiplication, establishes certain laws of correspondence, which, together with the facts he so adequately cites, have the closest bearing on the antecedents of longevity. Nevertheless it is to be noted that the term 'longevity' is not once used in these chapters, nor is the duration of individual life discussed directly at all. Did the nature of this essay permit, it would be perhaps the most satisfactory way of treating the question of longevity, to assume the contents of Mr. Spencer's volumes and to write a last chapter on the Duration of Individuals. This is not, however, the form which it is deemed right to adopt upon the present occasion, though frequent reference to and use of the views of this most eminent philosopher will be made.

Having dismissed the subject of books, let us consider for a moment the nature of the data which are available with regard to the duration of life. We shall find that the paucity and uncertainty of observations on this class of facts is something really extreme. Lord Bacon, in his Historia Vitæ et Mortis,' makes a remark which is true to this day:'De diuturnitate, et brevitate vitæ in animalibus tenuis est informatio, quæ haberi potest; observatio negligens; traditio fabulosa; in cicurribus vita degener corrumpit; in sylvestribus injuria cœli intercipit." To begin with man himself, we have sta

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tistics, individual assertions, general impressions, experiment. It might be supposed that statistics would furnish very valuable evidence on this matter; but, in the first place, it is only within certain European areas and a part of America that statistics relating to age are prepared, and the qualifications to which these are subject, from the shifting of population, are of a very complex character; further, there is a remarkable personal equation in the observers, who are at the same time the subjects of the enquiry into age, which it seems almost impossible fairly to estimate. Men do not tell the truth as to their age, either from ignorance or from deceitfulness. The ill-educated and the aged are specially likely to make false statements from ignorance, whilst that 'vanity which never grows old' affects equally the statements of old and young.

Individual assertions, taken alone and apart from the correction which the average of a vast number must ensure, are of course still less to be depended upon, and for the same reasons. General impressions, such as are imparted to us by travellers, by poets, and even historians, are of very small value when they relate to the duration of life, where it is so easy to confuse wear and one of its factors age. Experiment of what will ensure long duration of life in himself has been too rarely tried by man to make this class of evidence of any scientific value, whilst amongst

1 Buffon.

animals man seems never to have selected or endeavoured to produce longevity, probably because of its uselessness; had he done so, we might hope for some valuable facts from his experiments.

With regard to observations on the length of life of other animals, the certain knowledge is very small, only that tenure of life which is very brief being easily observed.1 The greatest uncertainty or even ignorance prevails as to the duration of life of even the commonest mammals, birds, and fishes; in most cases it seems only possible to say that it is not less than a certain period. This of course furnishes a limited means of comparison. A writer in the 'English Cyclopædia' says: 'Of the age to which the horse would naturally arrive, it is impossible to say anything satisfactory. Many have exceeded thirty, and some of them even forty, but from ill usage and over-exertion the majority come to their end before they have seen nine or ten years.' M. Flourens gives exceedingly wide ranges for many mammals in his book above noted, whilst it is obvious, if we consider the position of many wild animals, such as the larger

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1 We may naturally suppose that if we are ignorant with regard to man to the extent above shewn, still more à fortiori shall we be ignorant as to wild animals, to none of which has statistical examination been applied, nor probably can be in any but the rarest cases. It is clear, since animals do not carry the number of the years of their proper life marked on their bodies, like any of those specific characters which are structural, we can only form guesses as to this period from individual cases. 2 C. Knight's English Cyclopædia,' ArticleHorse.'

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carnivora, most birds, reptiles, fishes, and aquatic animals, that any suppositions as to their duration of life can rest on but few facts. In reply to enquiries, Mr. Charles Darwin writes that he has no information with regard to the longevity of the nearest wild representatives of our domesticated animals, nor notes as to the longevity of our quadrupeds.1 Mr. Thomas Bell, the author of most valuable works on 'British Quadrupeds,' 'British Reptiles,' and 'British Crustacea Podophthalmia,' in reply to special enquiry, writes that the opportunities of observation are few, and the results necessarily uncertain as to length of life in Reptiles and Crustacea.2 Dr. Gunther, of the British Museum, a most able ichthyologist and naturalist, remarks, in a letter in reply to enquiries,―There is scarcely anything positive known of the age and causes of death of various fishes.' So, too, in Mr. Yarrell's works little is said of duration of life; whilst in Mr. Gwyn Jeffreys' admirable treatise on the British Mollusca a similar absence of knowledge with regard to those animals is admitted. The Insects form a remarkable exception, since in a great number of them the duration of life is well known.3

1 Mr. Darwin very kindly furnished me with a note relative to the age of certain birds, which is quoted in the Table of Statements, which follows.

2 He, however, gives two facts which are mentioned in the Table of Statements.

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3 Only comparatively well known,' however, for the relative duration of life in different species of insects, involving a matter of months and days, is not known.

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