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It was the information given by the traveller on the diamond-mines worked in his day, that first drew Mr. Ball's attention to the subject of Tavernier's travels. The mines visited and described by him have long been abandoned, and even their very sites forgotten. With free labour, and at its present enhanced rates, diamondworking is no longer so remunerative as under the despotic governments of the seventeenth century, and it is within the recollection of the present writer that the working of one of the most productive mines of the former Golconda State was let on behalf of the British Government at the modest rental of 100 rupees. Tavernier gives it to be understood, indeed, that only four mines were worked, all of which he visited; but Mr. Ball tells us there is ample reason for believing that they were far more numerous than he had any conception of; and in an appendix he gives a full list of all the Indian localities at which diamonds have been obtained as far as is known, together with the geographical co-ordinates of all such as he has succeeded in identifying. Owing to the vagaries of phonetic spelling, and the ignorance of Indian geography on the part of many who have dealt with this subject, this identification has been far from easy. As amusing examples of the way in which localities have been confused by some previous writers, Mr. Ball tells us that "one author gives Pegu as a diamond-mine in Southern India; in the Mount Catti of another we have a reference to the Gháts of Southern India"; and he adds: "For some time I was unable to identify a certain Mr. Cullinger, who was quoted by one writer, in connection with diamonds. Will it be believed that this gentleman ultimately proved on investigation to be the fort of Kálinjar?"—a well-known historical fortress in Bundelkhand.

Indian diamonds are found exclusively in rocks of the Vindhyan formation or in the gravels of rivers that drain these rocks. The formation consists of sandstones, limestones, and other sedimentary rocks, certainly not more recent than the Lower Palæozoic age, but being unfossiliferous, their precise age cannot be determined. In Southern India the diamonds occur only in the Bánaganpili sandstone, at the base of the lower subdivision of the Vindhyan series, or in gravels derived from that bed. This is described by the authors of the "Manual of the Geology of India" as usually from 10 to 20 feet thick, consisting of gravelly, coarse sandstone, often earthy, and containing numerous beds of small pebbles. The dia. monds are found in some of the more clayey and pebbly layers, and in the opinion of Dr. W. King, the present Director of the Indian Geological Survey, they are innate in the rock. This view does not, however, appear to commend itself to the authors of the manual. In Northern India, at Panna, in Bundelkhand, the diamond bed is in the upper division of the Vindhyan series; but it is considered not improbable that here also the original nidus of the diamonds was, as in Southern India, a bed of the lower subdivision, pebbles of which occur in the diamond bed, and are extracted and broken up in the search for the gem.

As is well known, Tavernier examined, and in his book described and figured, the famous Great Mogul diamond, then in the possession of the Emperor Aurungzebe; and he has been often cited as a principal witness by those

who have discussed the question of the history of the Koh-i-noor. To this subject Mr. Ball devotes a long note in the appendix, arriving at conclusions which differ from those of Prof. N. S. Maskelyne, and indeed of most previous writers, with the exception of James Forbes, Major-General Sleeman, and Mr. Tennant. The argument is somewhat complex, and hardly admits of abstrac tion, and we must therefore refer those who are interested in the subject to the text of Mr. Ball's note. It will suffice here to indicate the main issues. They are concerned with the identification inter se of the three diamonds known respectively as the Mogul diamond, Baber's diamond, and the Koh-i-noor. The first of these, described and figured by Tavernier, is the largest diamond on re cord, and is stated to have weighed originally, before cutting, 900 ratis (an Indian weight still in use, but the value of which has varied greatly at different times and under different circumstances). When Tavernier saw it, it had been reduced by unskilful cutting to about two-fifths of its former size, and weighed only 379 ratis, which Mr. Ball computes to be equivalent to 268 English carats. Baber's diamond, of which Tavernier makes no mention, but which is equally historic, Mr. Ball thinks was probably retained by the imprisoned Shah Jehan, and acquired by Aurungzebe only after Shah Jehan's death. The weight of this stone is computed by Mr. Ball, from the statements of Baber and Ferishta, to have been 186 English carats. The weight of the Koh-i-noor when first brought to England was exactly the same as that computed for Baber's diamond. or, accurately, 186.06 carats. Now Prof. Maskelyne, General Cunningham, and several other writers regard these three stones as identical, and the former suggests that Tavernier's estimate of the weight of the Great Mogul diamond in carats (probably Florentine) was erroneous, and due to his having adopted a mistaken value for the rati. This view Mr. Ball is unable to accept Nevertheless he considers it probable that the Koh-i-noor is the remnant of the Mogul diamond, from which portions have been removed while it was in the possession of the unfortunate grandson of Nadir Shah, or some other of those through whose hands it passed before it was acquired by Runjeet Singh; and that Baber's diamond was a distinct stone, now in the possession of the Shah of Persia, and known as the Dariya-i-noor (sea of lustre), the weight of which is also 186 carats.

Mr. Ball's careful criticism of the available evidence. and his clear setting forth of the several steps of his argument, give weight to the conclusion at which he finally arrives, that will doubtless be acknowledged even by those who differ from him. But as regards the identity of the Koh-i-noor and the Mogul diamond, there remains one objection which, as it appears to us, Mr Ball has hardly adequately disposed of. If Tavernier's figure, as reproduced by Mr. Ball, represents at all faithfully the general form and especially the height of the Mogul diamond, it is difficult to see how a comparatively flat stone like the Koh-i-noor could have been obtained from it without a much greater reduction of its weight than the 82 carats which are all that his data admit of The lateral dimensions of the two stones accord fairly enough, so that any reduction of Tavernier's figured stone, to bring it down to the required size, could be

effected only by diminishing its height; in which case it would hardly correspond to his description of its form as that of an egg cut in two. The question can only be fairly tested by the weighment of a model constructed as nearly as possible in accordance with Tavernier's figure, and of such lateral dimensions as to be capable of including the Koh-i-noor. It may be that such a model, of the specific gravity of the diamond, would be found much to exceed Tavernier's reported weight of the stone, in which case the importance of his figure as an item of endence, would be greatly invalidated.

Whatever may be the final outcome of this controversy, Mr. Ball has done a good service to literature and science in re-translating Tavernier's work, in its careful editing, and in throwing light on much that has hitherto remained obscure. The result will certainly be that which he has anticipated, the vindication of Tavernier's claim "to be regarded as a veracious and original author."

OUR BOOK shelf.

H. F. B.

Star Lind By Sir Robert S. Ball, LL.D., F.R.S.
London: Cassell and Co., 1889.)

into, and a few experiments, illustrative of elementary
scientific principles, are well included. The work is
of the little details so
thoroughly practical; none
necessary to beginners have been omitted, whilst many
of the hints it contains may be of service to all who use
this optical instrument, whether it be for lecture purposes
or for recreation only.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE, No notice is taken of anonymous communications.]

Acquired Characters and Congenital Variation.

I Do not see that the Duke of Argyll's last letter in any way strengthens his position. The questions at issue with regard to evolution are now, I believe, thoroughly understood by biologists. Nothing, in my opinion, can solve them in the direction the Duke desires but the evidence of fact. And that, I can only repeat, is precisely what is not forthcoming. I am equally of opinion that the discussion has been worn threadbare. I should not myself have interfered in it, had it not seemed desirable to show that the motives attributed by the Duke to those who accept Darwinian principles were destitute of foundation.

This part of his position the Duke does not attempt to defend. As to the rest he merely restates what he has said before. His remarks fall under two heads, and I shall content myself with the briefest possible comment upon these.

(1) Acquired Characters.-The Duke gives what I presume he intends as a logical proof of the theorem that acquired characters are inherited. It may, I think, be formally expressed as follows:

developed latent congenital characters.
"It is always possible to assert that acquired characters are

THE author of this work is now so well known as a popular expounder of astronomical subjects that it is quite sufficient praise of his new book to say that it fully sustains his reputation. The book is described as “talks with young people about the wonders of the heavens," being founded chiefly on notes taken at his courses of venile lectures at the Royal Institution. Astronomy gives plenty of scope for the exercise of the imagination, and Dr. Ball takes full advantage of this. The book bonds with anecdotes and homely illustrations, calcuated to impress the facts on the memory as well as to excite wonder at them. The startling figures dealt with in astronomy are, as usual, converted into railway train utation, and otherwise illustrated. One new illustration ot the distances of the stars is that it would take all the Lancashire cotton factories 400 years to spin a threading of "acquired characters" has been clearly defined. They

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ng enough to reach the nearest star at the present rate ut production of about 155,000,000 miles per day. The regularities in the motion of Encke's comet are explained in an interesting dialogue between the "offending comet and the astronomer, in which the comet explains that is delay was due to the fact that Mercury was "meddlecome."

The only disappointing parts of the book are those which deal with astronomical physics. One point not ufficiently insisted upon is the now generally acknowledged meteoritic constitution of comets; a connection is rtainly suggested, but that comets are now supposed to be simply dense swarms of meteorites is not stated at all. Nebule, again, are described as "masses of glowing gas," notwithstanding the recent researches on the subject. The theory that meteorites are the products of ancient serrestrial volcanoes is also still adopted by Dr. Ball, without any consideration of the objections to such a view. The book is well illustrated, and will undoubtedly awaken an interest in the subject in all intelligent

readers.

The Magic Lantern: its Construction and Use. By a
Fellow of the Chemical Society. (London: Perken,
Son, and Rayment.)

IHE third edition of this little book has been issued,
and will be exceedingly useful to those who work with
tie lantern. Descriptions are given of the various
lights used in lanterns, from the oil lamp to the electric
arc; the methods of making simple slides are entered

It is admitted that congenital characters are inherited.
.. Acquired characters are inherited.

It will be observed in the first place that this is a mere a priori argument. And next that, while it is not denied by Darwinians that the organism is a complex of congenital tendencies, limitations, and possibilities, this is entirely beside the question. From Lamarck to Darwin, Weismann, and Lankester, the mean

are those changes of hypertrophy, extension, thickening, and the like, which are obviously due to the direct physical action of the these changes which Lamarck asserted were transmitted to the environment on the body of the individual organism. It was offspring; and it is this transmission which it is now maintained needs demonstration as a fact.

Let me give another illustration. I read the other day in the newspapers that the police of Paris have carried out an extremely interesting investigation. They have carefully ascertained the recognizable changes in the normal human organism produced by the prolonged pursuit of any particular occupation. The object was to obtain data for the identification of unknown dead bodies. The changes proved more numerous and characteristic than could have been supposed. They supplied, in fact, diagnostic marks by which the occupation of the individual could be accurately inferred. It seems to me impossible to have a more

admirable case of the direct action of external conditions.

I

ask, Is there any reason to suppose that these acquired characters would be transmitted?

This appears to me an extremely plain issue, as it is certainly an extremely important one. There is not the least reluctance on the part of Darwinians to face it squarely. But the Duke appears to me to deliberately evade it.

(2) Prophetic Germs.-It seems to me that we are somewhat at cross-purposes. The Duke admits that I have correctly quoted him as saying: "All organs do actually pass through rudimentary stages in which actual use is impossible.' When Prof. Lankester challenged the Duke to produce a single instance, he guarded himself by the remark: "The stages here alluded to are-if I understand correctly-ancestral stages, not stages in the embryological development of the individual. The Duke has never repudiated, as far as I am aware, that limitation of his meaning, if it be a limitation.

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And as he has

never responded to the challenge, I maintain that he has no right in a scientific discussion to reiterate a statement in support of which he has produced no definite observed evidence. He now returns the challenge to me. But it is no affair of mine. I simply take note of the fact that Prof. Lankester pointed out that the Duke's case collapsed unless the challenge was met, and that the Duke acquiesced by silence.

Just, however, as with the question of acquired characters, the Duke in defect of direct evidence now tries an a priori argument. He reminds us of the well known principle of embryology, some times called the recapitulation theory. Darwin states it in this form the embryo is "a picture, more or less obscured, of the progenitor, either in its adult or larval state, of all the members of the same great class."

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Now, of course, in the development of the individual organism, we have "a series of incipient structures on the rise for actual use," if by "on the rise" we mean in process of nutritive growth. This is, however, not necessarily true of the recapitulative structures which may or may not be temporarily utilized. When they are not so utilized they are mere survivals, and we know that survivals constantly so completely fall out of use, that by mere inspection it is often difficult to conceive what could have been their original function. I may give a single illustration. In flowering plants the homologue of the spore of the vascular cryptogams is still preserved. Within it, previous to fertilization, certain rudimentary structures are developed. It has been shown that these are the last recapitulative remnant of an independent series of structures developed outside the spore in the fern. In that type they form the prothallus, which possesses all the attributes of an independent organism, assimilates, respires, often reproduces itself asexually, and finally bears the sexual reproductive organs. All this in the flowering plant is not merely reduced to scarcely intelligible rudiments, but, in accordance with a well-known principle in embryology, it is thrown backwards in the order of development, and never emerges from the spore at all, instead of as in the fern being wholly external to and independent of it.

In this case we know the recapitulation and the thing recapitulated. We infer from their comparison that a fern-like plant was amongst the ancestry of the flowering plant. But I defy anyone, from a mere inspection of what happens in the latter, to form any idea of what happens in the former. From cases such as these it is obvious that the analogy between the development of the individual and the evolution of the race only holds for the broad facts of the sequence of stages, and does not give us any information as to the inutility of the structures of the ancestral organisms, or even, indeed, as to the precise period in their life when such structures made their appearance. The Duke's argument may now, I take it, be stated as follows:In the development of the individual organism, incipient organs are useless.

The development of the individual organism is a recapitulation of the evolution of the race.

.. Incipient organs in the evolution of the race are useless. I observe that the Duke's estimation of my logical powers is the reverse of flattering. I abstain, therefore, from criticizing this piece of reasoning. For my part I must confess I do not possess an a priori mind. No argument, however ingenious, is as convincing to me as accurately observed facts. If the Duke's convictions are laws of Nature, the objective verification ought to be forthcoming. W. T. THISELTON DYER.

Royal Gardens, Kew.

THE Duke of Argyll supports his assertion that "all organs do actually pass through rudimentary stages in which actual use is impossible" by reference to the stages of embryonic growth. Surely the assertion remains merely an empty repetition of the Darwinian position that the development of the embryo summarizes the morphological history of the race.

The modern dress coat has developed from a mere blanket, but even the useless parts of the modern coat can be easily shown to have had their use in some anterior forms of completed coat. The embryo, like the coat, preserves traces of evolutional stages at which what now appear useless characters were in reality actual useful characters.

What the Duke has to show is some instance of a completed organ in a completed organism, useless to that organism, not phases in the growth of an organ affording a blurred copy of some form of the organ existent at an anterior stage of the organism, and then useful to it. So far he has merely

confounded ontogenal steps of growth with phylogenal phases of plan. F. V. DICKINS. Burlington Gardens, February 3.

Eight Rainbows seen at the Same Time. THE following letter which I have just received from Lt Percival Frost of Cambridge, may interest your readers,

A statement that rainbows are produced not only by the sun itself directly, but by the image of the sun reflected from still water, is given in Prof. Tait's book un "Light." The pheno menon seems to have been observed by Halley in 1698 sec NATURE, vol. x. pp. 437, 460, and 483 for interesting con respondence on the subject).

The diffuse rainbow produced by the image of the sun re flected from a white cloud after sunset, described by Mr Scouller, is, I believe, a novelty. WILLIAM THOMSON

The University, Glasgow, January 31.

IN NATURE (January 23, p. 271) you give a letter from Mr. Sconlle describing an interesting case of a rainbow, due to the image of the sun in water, which, with the ordinary, primary, and secondary bows, make up (there being no secondary to that formed by the reflected sun) the three which he saw. Here is a short account of what I saw long ago, almost in prehistoric times, in Scotland, where such sights ought, according to your corre spondent, to be very commonly seen. I may mention that I saw at the same time, lasting some five minutes, eight wel' defined rainbows of one sort or another.

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In 1841, during the time of a long vacation party, spent at Oban, I walked out with my brother to Dunstaffnage and we were on the top of the Castle, somewhere between 3 and 4 p.m., on a day in the middle of August. No a breath of wind, bright sun over, I think, Lismore Lighthouse, dusky clouds all over Ben Cruachan and Cano!! Ferry; the sea in the bay (bounded by Dunstaffnage the west) as smooth as a pond. Gradually there appeare before us the astonishing sight of the aforesaid right distinc rainbows, viz. primary and secondary ordinary bows; pr mary and secondary bows by reflected sun; primary and

secondary bows formed by light from the real sun reflected from the water after leaving certain drops; primary and secondary formed by light from the sun reflected at the water, and, after leaving certain other drops, again reflected at the water. I have called the latter four distinct bows, because, although they looked like reflections of a solid set of four arcs, they were really formed by means of drops distinct from those which helped to make the first four bows. I append a sketch of what I saw. PERCIVAL FROST.

15 Fitzwilliam Street, January 29. [We have received other letters on the subject of Mr. Scouller's letter.]

Thought and Breathing.

I SEND you some extracts from the Sanskrit Yoga-sûtras which treat very fully of the prânâyâma, or the expulsion and retention of breath, as a means of steadying the mind.

A Yogi has first of all to assume certain postures which help him to fix his mind on certain objects. He cannot concentrate his mind while walking or running. He ought to assume a firm and pleasant position, one requiring little effort. To judge, however, from the description given of some of these postures, they would seem to us anything but pleasant.

When a Yogi has accustomed himself to his posture, he begins to regulate his breath-that is, he draws in the breath Through one nostril, retains it for some time in the chest, and hen emits it through the other nostril. The details of this process are given in the first chapter of the Yoga-sutras, sutra 37. Here the commentator states that the expulsion means the throwing out of the air from the lungs in a fixed quantity through a special effort. Retention is the restraint or stoppage of the motion of breath for a certain limited time. That stoppage is effected by wo acts-by filling the lungs with external air, and by retaining therein the inhaled air. Thus the threefold prânâyâma, including the three acts of expiration, inspiration, and retention of breath, fixes the thinking principle to one point of concentration. All The functions of the organs being preceded by that of the breath -there being always a correlation between breath and mind in their respective functions-the breath, when overcome by stopping all the functions of the organs, effects the concentration of the thinking principle to one object.

Rajendralal Mitra, to whom we owe a very valuable edition of the text and translation of the Yoga-sutras, adds the folwing remarks:-" All other Yogic and Tantric works regard the three acts of expiration, inspiration, and retention performed in specific order to constitute práâyâma. The order, however, is not always the same. . . . The mode of reckoning the time o be devoted to each act is regulated in one of two ways: (1) by so many repetitions of the syllable om, or the mystic mantra for nula of the performer, or the specific mystic syllables (vîja) of that mantra; (2) by turning the thumb and the index-finger of the left hand round the left knee a given number of times. The time devoted to inspiration is the shortest, and to retention The longest. A Vaishnava in his ordinary daily prayer repeats The Vija-mantra once while expiring, 7 times while inspiring, and 20 times while retaining. A Sakta repeats the mantra 16 imes while inspiring, 64 times while retaining, and 32 times *aile expiring. These periods are frequently modified.'

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The usual mode of performing the pranayama is, after assuming the posture prescribed, to place the ring-finger of the right hand on the left nostril, pressing it so as to close it, and to expire with the right, then to press the right nostril with the thumb, and to inspire through the left nostril, and then to close the two nostrils with the ring finger and the thumb, and to stop all breathing. The order is reversed in the next operation, and in the third act the first form is required. The Hathadipika says:"By the motion of the breath, the thinking principle moves; when that motion is stopped, it becomes motionless, and the Yogi becomes firm as the trunk of a tree; therefore the wind should be stopped. As long as the breath remains in the bly, so long it is called living. Death is the exit of that breath, therefore it should be stopped."

Some of the minor works on Yoga expatiate on the sanitary and therapeutic advantages of practising pranayama regularly at lated times. In America some spiritualistic doctors prescribe the same practice for curing diseases.

In India pranayama is only a means towards a higher objectnamely, the abstraction of the organs from their natural functions. It is a preliminary to Yoga, which consists in dharand, stead

fastness, dhyana, contemplation, and samadhi, meditation, or almost a cataleptic trance. These three are supposed to impart powers or siddhis which seem to us incredible, but which nevertheless are attested by the ancient Yogis in a very bona-fide spirit, and deserve examination, if only as instances of human credulity. I say nothing of modern impostures. Oxford, January 22. F. MAX MÜLLER.

IN connection with Prof. Leumann's recent researches into the relation between changes in respiration and changes in certain cerebral functions, it seems curious that the employment of deep and rapid respiration as an anesthetic has received so little attention. Some dentists order their patients to respire as quickly and fully as they can for a period which varies, I believe, from four to six minutes, although as to the exact duration I am insufficiently informed. At the termination of this period the patient becomes giddy, and to a great extent loses consciousness, when a short operation can be painlessly performed. The patient, while unable to move his arms, opens his mouth at the order of the operator. I have heard of no casualties or evil effects from this mode of treatment. W. CLEMENT LEY.

Chiff-Chaff singing in September.

DURING more than forty years' observation of the singing of birds, I have invariably heard the chiff-chaff singing in September, although the song is much less frequently repeated than in the spring. In connection with this observation I may mention that both the male and female birds appear to be always mute for two or three days after their spring arrival in Northern Europe. W. CLEMENT LEY. Lutterworth, January 31.

Foreign Substances attached to Crabs.

I HAVE read in recent numbers of NATURE some letters on sponges attached to crabs.

There are two crabs on the east coast of Australia-one of them allied to Dromia vulgaris-which cover themselves with sponges or with a composite Ascidian. I have in one case counted no less than seven species of sponges on one individual crab.

The Ascidian referred to is usually from ten to thirty times as large as the crab to the back of which it is attached.

Among the specimens brought by me from Australia, and now deposited in the National Collection of the British Museum, there are some of these crabs with sponges and Ascidians attached.

These might, perhaps, be interesting to your correspondents on the subject. R. v. LENDENFELD.

University, Innsbruck, January 25.

Foot-Pounds.

"A. S. E." will find moments, of resistance, of bending, or of in any treatise on civil, mechanical, or marine engineering, on turning, expressed in foot-pounds (often inch-pounds or foot tons) architecture, land or naval, and, in fact, in every treatise on real mechanics he may consult. Why, then, should a different terminology be adopted in a Civil Service examination paper? In metric units, moments are given in kilogramme-metres or -centimetres; but in the C.G. S. system I do not suppose it is suggested to measure moments of dyne-centimetres in ergs. February 3. A. G. GREENHILL.

IF "A. S. E." will push his researches further, he will fin 1 that in Government dockyards the stability moment on ships is V. calculated in foot-tons. February 3.

PROF. WEISMANN'S THEORY OF HEREDITY,

IN NATURE of October 24, 1889 (p. 621), appeared a

criticism by Prof. Vines of my essays on heredity and allied subjects. I should be glad to reply briefly to his objections, and the more so as I hope thus to be able to place the scientific problems at issue in a somewhat

clearer light. With regard to the immortality which I attribute both to the unicellular organisms and to the germinal cells of the multicellular, if I understand Prof. Vines aright, he does not attack the proposition itself, but has simply overlooked the explanation in my book of the way in which mortal organisms arose out of immortal in process of phyletic development, a process which must have taken place if the Protozoa have developed in the course of the world's history into the higher Metazoa,-"the first difficulty is to understand how the mortal heteroplastides can have been evolved from the immortal monoplastides." My explanation was simply that which appears to be the true one for the origin of every higher differentiationnamely, the division of the cell-mass of the Protozoan, on the principle of the division of labour, into two dissimilar halves, differing in substance, and consequently also in function; from the one cell which performed all functions comes a group of several cells which distribute themselves over the work. In my opinion, the first such differentiation produced two sets of cells, the one the mortal cells of the body proper, the other the immortal germ-cells. Prof. Vines certainly believes in the principle of the division of labour, and in the part that it has played in the development of the organic world, as well as I; but it seems to him that this division of a unicellular being into somatic and germinal cells is impossible, and that my explanation of the process by dissimilar division is inadequate, because it strikes him as “absurd to say that an immortal substance can be converted into a mortal substance."

There certainly does seem to be a great difficulty in this idea, but in reality it arises simply from a confusion of two conceptions-immortality and eternity. That the Protozoa and the germ-cells of Metazoa are in a certain sense immortal seems to me an incontrovertible proposition. As soon as one has clearly realized that the division of a monoplastid is in no way connected with the death of one part, there can be no further question that we have to do with individuals of indefinite duration; but this in no way implies that they possess an eternal duration; on the contrary, we imagine that they have all had a beginning. The conception of eternity, however, extends into the past as well as the future; it is without beginning or end, and does not affect the present question; it is an entirely artificial conception, and has no real and comprehensible existence; to express it more accurately, eternity is merely the negation of the conception of transitoriness. Of the objects with which natural science deals, none are eternal except the smallest particles of matter and their forces, certainly not the thousandfold semblances and combinations under which matter and force meet us. As I have said years ago, the immortality of unicellular organisms, and of the germ-cells of the multicellular, is not absolute but potential; it is not that they must live for ever as did the gods of the ancient Greeks -Ares received a "mortal wound, and roared for pain like to ten thousand bulls, but could not die; they can die-the greater number do in fact die-but a proportion lives on which is of one and the same substance with the others. Does not life, here as elsewhere, depend on metabolism-that is to say, a constant change of material? And what is it, then, which is immortal? Clearly not the substance, but only a definite form of activity. The protoplasm of the unicellular animals is of such chemical and molecular structure that the cycle of material which constitutes life returns even to the same point and can always begin anew, so long as the necessary external conditions are forthcoming. It is like the circulation of water, which evaporates, gathers into clouds, and falls as rain upon the earth, always to evaporate afresh. And as in the physical and chemical properties of water there is no inherent cause for the cessation of this cycle, so there is no clear reason in the physical condition of unicellular organisms why the cycle

of life, ie. of division, growth by assimilation, and repeated division, should ever end; and this characteristic it is which I have termed immortality. It is the only true immortality to be found in Nature-a pure biological conception, and one to be carefully dis tinguished from the eternity of dead, that is to say unorganized, matter.

If then this true immortality is but cyclical, and is conditioned by the physical constitution of the protoplasin. why is it inconceivable that this constitution should be under certain circumstances and to a certain extent. 20 modified that the metabolic activity no longer exactly follows its own orbit, but after more or fewer revolutions comes to a standstill and results in death? All living matter is variable; why should not variations in the protoplasm have also occurred which, while they fulfilled certain functions of the individual economy better, caused a metabolism which did not exactly repeat itself, .. sooner or later came to a condition of rest? I admit that I feel such a descent from immortality into mortality far less remarkable than the permanent retention of immortality by the monoplastids and germ-cells. Small, indeed, must be the variations in the complicated qualities of living matter to bring in their train such a fall; and ver sharply must the essentials of its constitution be retained for metabolism to take place so smoothly without creating in itself an obstacle to its own continuance! Even if we cannot penetrate into the mysteries of this constitution, still we may say that a rigorous and unceasing natural selection is unremittingly active in maintaining it at such an exact standard as to preserve its immortality; and every lapse from this standard is punished by death.

I believe that I have proved that organs no longer in use become rudimentary, and must finally disappear solely by "panmixie"; not through the direct action of disuse, but because natural selection no longer matains their standard structure. What is true for an organ is true also for its function, since the latter is but the expression of the qualities of material parts, whether we can directly perceive their relations or not. If, then, as we saw, the immortality of monoplastids depends on the fact that the incessant metabolism of their bodies is eve returning exactly to its starting-point, and produces no such modifications as would gradually obstruct the repe tition of the cycle, why should that quality of the living matter which causes immortality-nay, how could it be retained-when no longer necessary? It is obvious that it was no longer necessary in the somatic cells of the heteroplastids. From the instant that natural selection relaxed its watch on this quality of immortality began the process of panmixia which led to its abolition. Prof Vines will ask, How can one conceive of this process? I answer, Quite easily. When once individuals arose among monoplastids, in the protoplasm of which occurred such variation in chemical and molecular constitution as to result in a gradual check on the metabolic cycle, it would happen that these individuals died; a permancut variety could not grow out of such variations. But d there arose among heteroplastids individuals with a similar differentiation of the somatic cells, the death of these cells would not be detrimental to the species, since its continuance is ensured by the immortal germ-cells Upon the differentiation into germinal and somatic cells natural selection was, speaking metaphorically, trained to bear on immortality of the germ-cells, but on quite other qualities in the somatic cells-on motility, irritab lity, capacity for assimilation, &c. We do not know whether the attainment of these qualities was accompanied by a constitutional alteration which caused the loss of immor tality, but it is at least possible; and, if true, the somatic cells will have lost their immortality even more rapidly than through the unaided action of panmixia.

In the fourth essay of my book, I have cited the two Volvocinean genera Pandorina and Volvox as examples

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