but perfectly regular differences. The position of the absorption bands varies with the mass of the colourless ion, and certain other facts have been observed of the same character. Prof. Kayser reviews most carefully the whole of the evidence of absorption spectra that has been brought forward both for and against the ionic hypothesis; he finally concludes that Ostwald's theory, namely, that the behaviour of dilute aqueous solutions of coloured metallic salts is due to the colour of the ions, is untenable. Such an authoritative statement, based on experimental evidence, is very striking and worthy of careful consideration by physical chemists.

The third chapter has been written by Prof. Hartley,

and deals with the relation between absorption and

chemical constitution. It contains an excellent résumé of all the work which has been carried out, chiefly by Prof. Hartley himself, on the bearing of ultra-violet absorption to molecular structure. The value of this work is too well known to need emphasising here, and it is not too much to say that this is one of the most important branches of spectroscopy, and one that is certain to lead to results of farreaching importance in organic chemistry.

The two last chapters deal in detail with absorption spectra; in the fourth chapter are described the spectra of many substances, selected either because they are of some practical use, or because they possess some special point of interest, while the fifth and last chapter contains an alphabetical list of all substances the absorption of which has been measured.

Of the great value of this book it is impossible to speak too highly; it is sufficient to say that it will rank as the standard work upon absorption. All who read it will appreciate to the full the great care Prof. Kayser has bestowed upon it and the immense labour involved in dealing with the mass of literature upon the subject. E. C. C. B.

OUR BOOK SHELF. Identification por las Impresiones digito-palmares (La Dactiloscopia). By Dr. Alberto Yvert. Pp. 111. (La Plata : A. Gasperini, 1905.) THIS work is the thesis presented by the author to the University of Lyons in order to obtain a doctor's degree in medicine. It deals, firstly, with the uses to which identification by means of finger-prints can be put by the detective, and shows how the fingers of the murderer leave their impression printed in the blood of his victim; while those of the burglar may be brought to light on the window through which he has passed, by the simple expedient of breathing on it, and may be indelibly recorded by means of hydrofluoric acid; and, lastly, the finger-marks of the forger may be revealed on the cheque which he has forged, by means of Mr. Forgeot's method. This last record is produced, first, by the sweat of the fingers that rest on the paper, which, when it evaporates, leaves an invisible print behind it in the salts which were contained in it. This may be made to appear by the application of an 8 per cent. solution of nitrate of platinum, which is affected by these salts in such a way that it blackens when exposed to light.

The author proceeds subsequently to the most important part of his work-a summary of the

principal methods of classification of finger-prints. He commences with a somewhat inadequate descrip tion of the original system, which, as is well known. is that of Francis Galton; he then goes on to treat with much fuller detail some of the various systems which are based on it. Among these are included that of M. E. K. Henry, which has been adopted by M. Windt, chief of the Identification Service of the Police in Vienna; that of M. Pottecher, chief of the Immigration and Identification Service in Saigon; and of Señor Vucetich, director of the Identification Service in La Plata. It is the last system which is preferred by the author. It consists in dividing all finger-prints into four types, which he names as follows:-(1) Arco-arch; (2) Presilla interna= internal loop; (3) Presilla externa external loop; These terms are (4) Verticilo or Torbellino = spiral. descriptive of the figures formed by the lines situated near the centre of the palmar surface of the distal phalanx of each digit. As all ten fingers are taken into account in the classification, and as each may be of any of the above four types, there are 4* (1,048,576) classes defined in this way. The minute details of the arrangement enable one to distinguish between different members of the same class. The pamphlet concludes with a useful bibliography. E. H. J. S.

Science in South Africa: a Handbook and Review. Prepared under the auspices of the South African Governments and the South African Association for the Advancement of Science. Edited by the Rev. W. Flint and J. D. F. Gilchrist. Pp. x+480 (Cape Town, Pretoria, and Bulawayo: T. Maskew Miller, 1905.)

THOSE members of the British Association who were fortunate enough to visit South Africa this year cannot fail to have benefited by this useful and handsome volume. To those who were unable to accompany the association, but who take an interest in scientific work in South Africa, this "index book will be a great boon. Of late years, South African scientific literature has increased at a great rate, but the material frequently lies scattered in numerous publications often difficult of access, while so many divergent opinions on the same subject have been expressed that the student is apt to be bewildered. From the present volume the status quo of scientific research in South Africa can be ascertained. A longfelt want is thus supplied, and if the scientific literature is to increase at the same rate in the future as it has in the immediate past, a year-book on similar lines would be of inestimable value.

The cost of publication of the present volume has been defrayed by the various South African Governments. In doing this they betray an enlightened policy, for there can be no question that it will direct attention to the vital importance of scientific knowledge in a country so vicariously treated by nature as South Africa, where the natural products are dis tributed in such a way that they can only be utilised by the application of the discoveries of modern science. To those so trained, South Africa becomes a land of fertile promise.

The present volume is arranged in eight sections dealing with physical, anthropological, zoological botanical, geological, mineralogical, economic, educational, and historical problems. The sections and subsections are the voluntary contributions of actual workers, to whom the editors have allowed con siderable latitude as to the method of treatment In some cases the subjects are dealt with historically, in others from the practical point of view. volume contains numerous illustrations, among which

The

the handsome coloured plates of blue ground and diamonds of various shapes and colours, presented by Mr. Gardner Williams, stand out conspicuously.

While it is evident that much has been achieved, it is equally certain that in some branches only a start has been made. In fact, the dominant feeling produced by reading the several interesting articles is one that should inspire the greatest hope and enthusiasm among scientific students in this country and throughout South Africa. Here lie new worlds of unknown possibilities. As yet we stand only on the threshold. Far off glimpses of a wonderful country have been obtained, but it is the sight of a Kilimanjaro enshrouded in mist, not of the unclouded mighty mountain-mass. W. G.

Stone Gardens. By Rose Haig Thomas. Pp. xii and plates. (London: Simpkin, Marshall, Hamilton, Kent and Co., Ltd., 1905.)

AN old wall sheltering such plants as are accommodating enough to grow in such a situation is often a delight; but to undertake the formation of a "stonegarden" in the way suggested by the author is to run counter to all our notions of the amenity and purpose of a garden. Various "designs" are offered for adoption, such as a lyre-shaped outline made of paving stones with flower-beds representing the strings, and separated by narrow strips of stone.

Another design shows three snakes intertwined, each snake made of flat stones of a different tint from its neighbour. The spaces between the serpentine convolutions are filled in with flower-beds. Other designs are more appropriate to a formal or architectural garden.

Of course, there is no disputing upon points of taste, and each garden-lover must exercise his or her fancies according to circumstances and in obedience to individual proclivity. But if the designer intends to furnish a model for other people to adopt, then we expect there will be comparatively few garden-lovers who will share the author's taste or feel inclined to adopt her suggestions.

Be this as it may, the author gives very clear directions as to how her designs should be carried out, and very judicious instructions as to the plants to be selected and the method of planting them. Provided these be properly carried out, kindly nature will do her best to conceal the flags and stones, and if the author's designs are somewhat interfered with in the process, that will not be a matter for regret on the part of most garden-lovers. The work is in quarto, with fourteen designs in colour.

Oblique and Isometric Projection. By John Watson.
(London:
Pp. iv +59.
Edward Arnold, n.d.)

Price 38. 6d.

IN defining the forms and dimensions of solids by means of scale drawings, a very useful method in certain cases is that of metric projection whereby three systems of parallel edges of the solid are represented on paper by lines parallel to three axes drawn in arbitrarily selected directions, and to any three scales also independently chosen. The author deals only with isometric projection, and considers two cases, first, when the projection is orthogonal, secondly, when the projectors are oblique with the plane of projection taken parallel to a face of the solid, so that figures parallel to this face appear without distortion. The best part of the book is probably the chapter giving examples, mostly of joints in woodwork, used by the author in conducting classes in manual training; but it is doubtful whether it was worth while to publish a book of such limited scope,

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.]

Eclipse Phenomena.

No opportunity for discussion was given at the Royal Society meeting last Thursday, but the following brief notes may be suggestive and possibly useful.

The particles in the corona which reflect solar light to us are presumably moving very fast away from the sun, and accordingly are illuminated by light of apparently extra-long wave-length. This light, thus lowered in refrangibility, they will emit; and inasmuch as they are probably moving at all sorts of speeds, we might expect that Fraunhofer lines would be encroached upon and blotted out from the resulting emission, especially as some particles would have a component of velocity towards us and others away from us.

If any of the particles are emitted with anything like the speed of some of those from radium, the maximum change of frequency to be expected would be great.

Particles illuminated by rays normal to our line of sight will send us a plane polarised beam, but when the illuminating rays are oblique to the line of sight, as may be the case from some of the longer streamers, then the polarisation would be only partial.

How far single electrons may be able to resist the forced vibrations of light-waves, and thus become themselves polarised sources, is a matter on which I hope to try some experiments. The illumination in which they are immersed near the sun is very intense.

The circular or ring appearance seen in the midst of the corona in some photographs, with geometric centre at a distance from the apparent centre of explosion, looked to me like a gigantic vortex ring. I see no reason why a sun-spot should not eject such rings occasionally. OLIVER LODGE.

Geometry of Position.

IN connection with the review of Mr. Wilson's recent book, on p. vi. of your supplement last week, may I direct the friendly attention of the reviewer and your readers to an old paper of mine in the Philosophical Magazine for November, 1875, where some of the theorems referred to are given. I myself have found a slight modification of the rapid system of writing chemical formulæ there advocated, extremely useful, and should like to advocate its use by elementary students of organic chemistry-but that is another matter. OLIVER Lodge. October 20.

Eclipse Predictions.

THE discrepancies referred to by Mr. J. Y. Buchanan (p. 603) as existing between the French and British predictions for the recent total eclipse of the sun are due simply to the fact that a different value of the moon's diameter is adopted in the Connaissance des Temps from that in the Nautical Almanac, the former being about 2"-7 greater than the latter. Hence the breadth of the zone of totality and the duration of totality on the central line are greater in the French than they are in the British ephemeris. But there is no occasion to impute mistake to the French calculators. They merely assume a value of the moon's diameter that is, in my opinion, too large for eclipse

purposes.

October 20.

A. M. W. DOWNING.

Chelifers and House-flies.

Ir may be that the view suggested in my letter to NATURE of August 31, that the association of the Chelifer with the house-fly is to the advantage of the former in providing it with a wider geographical distribution, is not

sound. I believe it is, but at the same time admit that there is not sufficient evidence at present to prove that the association is of material advantage to the species.

The important point to determine, however, is whether

the Chelifer is or is not a parasite on the house-fly. It is fully recognised now that house-flies play an important part in the distribution of the germs of certain diseases that affect mankind. Any animal, therefore, that injures or destroys the flies may assist in checking the spread of disease. But if, as Mr. Pocock suggests, the object of the Chelifer is to feed upon the acarine parasites of its host, it serves rather as a friend than a foe to the fly, and should certainly not be called a parasite.

There is no anatomical reason for believing that the Chelifers that have been found on flying insects are specially adapted to a parasitic mode of life, nor is there any evidence that the house-flies they are attached to are infested with mites or any other skin parasites. If the Chelifers are not parasitic on the flies, and there are no mites for them to attack, how can the association of the two forms be accounted for otherwise than by the transportation hypothesis?

Since I wrote my last letter to you I have found that this matter has been most fully discussed by Mr. Kew in his article on Lincolnshire Pseudoscorpions in the Naturalist for July, 1901, and I would refer readers of NATURE who are interested in the subject to that paper for fuller particulars. SYDNEY J. HICKSON.

University of Manchester, October 21.

66

The Rudimentary Hind Limbs of the Boine Snakes. IT is a well known fact that the pythons and boas and some allied forms among snakes possess rudiments of hind limbs, these vestiges-to quote Boulenger's Catalogue of Snakes in the British Museum "-" usually terminating in a claw-like spur visible on each side of the vent. These structures are always mentioned in general works upon Ophidia, such as Hoffmann's account of the serpents in vol. vi. of Bronn's "Klassen und Ordnungen des Thierreichs," and Gadow's "Reptiles and Amphibians" in the " Cambridge Natural History. But in none of the three treatises to which I refer is there any further account "claws 99 of the or spurs." It is merely stated that they are present. It is not mentioned in these works, nor in some others which I have consulted, that the claws in question offer valuable sexual characters by the aid of which individuals can be referred to their proper sex, at least in certain Boidæ. The fact that these characters have been so largely overlooked is perhaps due to the slight stress laid upon them by Duméril and Bibron (Erpétologie Générale, vol. vi., 1844), who, however, did direct attention to the occurrence of differences in these organs between the two sexes in a number of Boidæ. But they speak of the claws merely as being "d'une très petite dimension chez des femelles,' and as plus développés chez les males que chez les femelles." The first of these quotations refers to Eunectes, the second to Boa. The differences, however, in Eunectes notaeus are greater. In this southern anaconda, of which several specimens were lately deposited in these gardens by the Hon. Walter Rothschild, there is in the male a sharp curved claw turned downwards and ridged along its lower surface. In the female, on the other hand, the representative of this claw is not a claw at all strictly speaking-if, that is to say, we mean by a claw a nail-like structure which is curved and compressed and ends in a sharp point. In the female there is a straight, blunt, horny process distinctly unlike the sharp claw of the male. In two young examples of this anaconda, which are females, the same type of horny structure is found as in the adult female. In the allied genus Eryx there are still greater differences between the two sexes. FRANK E. BEDDARD. Zoological Society's Gardens, October 18.

A Rare Game Bird.

MR. SAWBRIDGE (p. 605) has raised one of the most perplexing points connected with bird-migration. I cannot answer for the eastern counties of England, but here, in the south-west of Scotland, we are still further from the headquarters of the quail than he is. Fifty years ago quails bred regularly in western Galloway; as a boy I recollect that two or three brace were quite a common complement to a September bag. Indeed, when a

cheeper or undersized partridge was shot, Put it down as a quail!" was the usual comment. These birds gradually disappeared; the last that I myself shot was about the year 1868; but an odd one has been obtained here and there in the district ever since. One, I know, was shot last month in the neighbourhood of Newton Stewart, and was reckoned such a curiosity that it was sent to the bird-stuffer. I am sorry that I do not know whether it was a young or an old bird. Besides this, other instances, if I mistake not, have been recorded in the Field from different parts of the country.

As to the cause of the general disappearance of quails from this district, there have been many speculations, the commonest notion being that the supply is so heavily taxed in the Mediterranean region that few birds escape to the north. Truly, when one considers the enormous consignments of quails to London, Paris, &c., there is no reason for surprise that the migrants should dwindle in number. I have a vague recollection of being told in boyhood that about the year 1838 there was a large influx of quails into Galloway, and that they had bred there ever since, but in numbers annually decreasing. It is conceivable that a storm-driven flock may have been carried out of their bearings, and, finding food abundant and climate endurable, if not altogether congenial, remained as colonists, but that our wet summers have proved adverse to their young being reared. The fluctuation in the stock of partridges caused by the character of different seasons is very remarkable, and evidently neither the numbers nor the constitution of our quails have enabled them to survive adverse conditions of temperature and rainfall. This makes the sporadic occurrence of individuals at long intervals all the more remarkable and perplexing.

HERBERT MAXWELL.

Monreith, Wigtownshire, October 22.

On a New Species of Guenon from the Cameroons. A CHARMINGLY docile species of guenon, obtained by Cross, of Liverpool, from the Cameroons, in West Africa, and recently submitted to me for identification proves to be undescribed. I propose for it the name Cercopithecus crossi, in compliment to the courteous proprietor of that large and well known importing house of wild animals, and for popular use the same of Cross's guenon. The animal is a male, apparently nearly full grown, but not entirely adult, as the condition of its teeth indicate. It is very similar to C. moloneyi of Sclater, in general appearance, in having the broad rufous lower back, but differs in having a large and bushy pure white beard, white throat, and bushy whiskers of black hairs ringed with white; the band across the forehead deep black instead of fulvous; sides of head speckled black and white; underside of body sooty-black speckled with white; the tail not deep black except at tip, but speckled black and white like the upper part of the back; the black on the forearm externally does not extend to the shoulder, and not much beyond the elbow; the outer aspect of thighs is black slightly peppered with white; the inside of arms below the elbow black, higher up sooty-grey: inside of hind limbs sooty-black.

The top of the head is black, the hairs sparsely ringed with white; the face, cheeks, and ears quite nude and purplish black in colour; long superciliary hairs are present; the callosities are small and purplish sooty-grey

in colour.

From C. albigularis (Sykes's guenon) the present species differs in wanting the yellowish wash on shoulders, fore and hind limbs, and in having a brindled and not a black tail. HENRY O. FORBES. The Museums, Liverpool, October 12.

The Absorption Spectrum of Benzene in the Ultra-viole: Region.

WE were glad to see in NATURE of October 5 a letter from Prof. Hartley in which he points out the near agree ment between our measurements of the bands in the absorption spectrum of benzene and those made by Prof Dobbie and himself. He also directs attention to the work of Friederichs, who, in the case of benzene vapour,

finds the position of these bands to be consistently nearer to the red end of the spectrum. The difference in the position of the bands in the spectrum of benzene vapour and of benzene in solution only proves, of course, the applicability of Kundt's rule. We are also pleased that Prof. Hartley has been able to see the second band on our list (2656), which, coupled with the fact that Friederichs has also measured it, we feel is a most important confirmation of our observations.

As regards the eighth band (A=2330) which has been measured in the absorption spectrum of benzene vapour by Friederichs (whose work we were, of course, unaware of when we wrote our paper), we have made a most careful search for it. We have re-examined our original plates and have taken several more photographs, but have been unable to find any trace of it. We must therefore conclude that it is absent from the spectrum of benzene in alcoholic solution.

There is one other point in Prof. Hartley's letter; he says we have overlooked some points of importance in his paper with Prof. Dobbie when we state that they only found six bands. It is quite true that in their paper Hartley and Dobbie refer in their table of measurements to another band of very short persistence which they mark as doubtful at 5 mm. thickness of N/10 solution, and very doubtful at 4 mm. thickness. In the letterpress, however, they speak of only six bands, and in all later publications benzene is stated to show six absorption bands. In the British Association report, and even in Prof. Hartley's paper to the Chemical Society on May 17 of this year, he speaks of six bands (Chem. Soc. Proc., xxi., 167). We therefore assumed that Prof. Hartley, on further consideration, had concluded that this doubtful band was not a true benzene absorption band. As we ourselves had seen no trace of this band, we in our paper before the Chemical Society (Trans. Chem. Soc., lxxxvii., 1332) stated that Hartley and Dobbie had found only six bands.

Prof. Hartley's ideas and work upon the absorption spectra of organic compounds in the ultra-violet are of the greatest importance; he was the first to show how the constitution of certain compounds could be established by this means. Prof. Hartley's method of "testing molecule by means of its absorption spectrum, we sure, will prove of the greatest possible value in the hands of chemists. E. C. C. BALY. J. NORMAN COLLIE.

University College, October 12.

Action of Radium Salts on Gelatin.

a

are

HAVING Occasion to give a demonstration of the properties of radium some little time ago, I determined to attempt the preparation of some of the organisms as described by Mr. J. Butler Burke.

The method employed was to sprinkle a few specks of the radium salt upon the surface of some sterilised gelatin contained in a test-tube, and then to await development. That did not take long. Almost at once a faint cloudiness appeared to start under the speck of salt which extended downwards into the gelatin, in some cases after twentyfour hours reaching the depth of one centimetre. No heating was required to bring about this "growth,' " which resembled to the unaided eye an ordinary mould. The experiment was made with radium preparation of varying degrees of activity, but it was soon observed that the degree of activity in the salt had little influence on the growth, a salt of radium barium bromide containing 11000 of its weight of active salt being nearly as efficacious as one containing 1/100. (The more pure specimens which I possess were too precious to experiment with.)

As the specimens used were composed chiefly of barium salt, it occurred to me that it might be interesting to try the effect of the pure barium salts on the gelatin. This was done, with the surprising result that the growths were just as easily obtained as with the radium preparation or even more so. I have tested all the barium salts at my disposal, and find the following produce the effect :Barium, oxide, dioxide, chloride, bromide, iodide, nitrate, acetate, tartrate, and sulphovinate, while the phosphate,

Thus the

was

as

carbonate, sulphate, and borate do not act. soluble salts are active, and the insoluble ones inactive. The method adopted for the experiments follows:-Some clear gelatin was poured on to a glass slip and allowed to set. A tiny speck of the salt was placed on the gelatin and covered with a thin glass. This slip was then placed on the stage of a microscope and examined with a 1-inch power. At once the " growth was seen to shoot out from the speck, and it appeared to consist of bubbles, some large, but most of them very small. Half an hour afterwards the speck had dissolved, leaving in its place a nebulous patch many times the size of the speck. The action of barium iodide is particularly rapid, while that of the hydrate is rather slow. I have tried uranium and thorium salts, both of which affect the gelatin rapidly, but do not produce the " growths." The action of these salts upon gelatin seems to point out an interesting field of inquiry, which I propose to follow. W. A. DoUGLAS RUDge.

Woodbridge School, Suffolk.

The Problem of "Shadow.bands." SUBSEQUENTLY to the Algiers eclipse of 1900, it occurred to me that the shadow-bands visible at times of total solar eclipse might be merely another aspect of the "boiling distortions of the sun's limb inseparable from daily observations. The last few years have therefore been employed by me in studying the characteristics of "boiling with the view of making a direct comparison of evidences at the first opportunity. This opportunity presented itself in the recent total solar eclipse observed by me at Cás Catalá, in Mallorca, on August 30 last.

Employing Carrington's method" of projecting the sun's image with a small telescope, the first observation made at about 10 a.m. recorded the existence of two distinct layers of cloud, the lower one travelling N.E. by S.W., and the upper one W.S.W. by E.S.E., giving confused and erratic boiling." Further observations revealed an increased prevalence of the N.E. cloud system, but the drift from W.S.W. was still in evidence. At 11.35, however, it transpired that the W.S.W. system alone prevailed, and all trace of the drift from N.E. had abated. Continuing the observation without any relaxation throughout the phase of partial eclipse until within a few minutes of totality, I was able to ascertain that the "boiling movements along the advancing limb of the moon were throughout absolutely in agreement in every particular with the movements of distortion affecting the still uncovered limb of the sun. Observations by projection were abandoned at 1h. 18.0m. for the purpose of securing a naked-eye view of "shadow-bands.' A very successful view of these was secured. Their direction of flight determined on the spot, and afterwards corrected by Dr. Hunter, of Edinburgh, by the compass, proved to be W.S.W. by E.S.E. It is noteworthy that at Palma, where the eclipse conditions were marred throughout by the cloud bank that had threatened to overwhelm us at Cás Catalá (only four miles S.W. of Palma), the shadow-bands were observed to take a direction N. 30° E. by S. 45° W. CATHARINE O. STEVENS.

66

Bradfield, Berks, October 20.

EXPERIMENTS ON VARIATIONS OF LEPI

DOPTERA BY ENVIRONMENT.

AN N important addition to the numerous papers of recent years recording experiments as to the influence upon the forms of living beings of their environment has lately been published. In this paper the inquiry is concerned only or chiefly with varieties in the pigmentation of Lepidoptera. The author enumerates as among the agents to which change in this pigmentation is to be ascribed "intensity of light, temperature, nutrition, humidity, dryness, electricity, and other meteorological phenoHis references to the literature on these subjects are very useful. The suggestion that mechanical movement, jarring, of pupæ, might cause effects analogous to those of temperature is mentioned, but this has long since been abandoned. M. Pictet divides the variation of pigmentation into two opposite types, the

mena.

66

one

99 albinism, by which red can pass into yellow and even into white, the other "melanism," by which red passes into brown and, as an extreme, into black; and this classification is kept in view all through the description of his experiments and their results. So is a theory which he puts forward, though with diffidence, that caterpillars in general were originally adapted to live only on certain special plants or trees, and afterwards, owing to finding themselves, as the result of migration or otherwise, where these were not to be had, adapted themselves to many other kinds, so as to become more or less polyphagous, still, however, in nature attaching themselves by preference to special food plants, called in this paper their normal or ancestral ones.

M. Pictet's treatment of this subject can be best illustrated by an extract:-" Lasiocampa quercus, known from the time of Linnæus as feeding almost exclusively on the oak, as indeed its name indicates, and the leaves of some trees and hedge shrubs, is now found frequently on ivy, poplar, sallow, birch, heath and arbutus." He does not always say what the normal food plant is, as in the case of Phalera bucephala, of which he states that it absolutely refuses to eat any but

evergreen which became widely distributed in Europe during the last century. Though, as stated, it is left uncertain in some cases what M. Pictet considers the normal food plants to be, that creates little or no difficulty in appreciating most of his experiments, as the kinds of food plants which in these experiments were substituted for the foods well known to be usual were so different that they may certainly be distinguished as abnormal; for example, when walnut or laurel, or low plants such as sainfoin (Onobrychis sativa), dandelion, lettuce, or salad burnet (Poterium sanguisorba) are substituted for any of the ordinary forest trees.

its normal food. In England it is found on lime, elm, willow, and many other forest trees at least as freely as on oak, and there is a record of a company found on laurel. Oak is given as the normal food of Biston hirtarius (found in England on a great variety of forest trees), gooseberry and spindle tree (Euonymus europaeus) as those of Abraxas grossulariata. In England this species is found in abundance also on blackthorn, &c., and it has of late years addicted itself to the Euonymus japonicus, an

1 "Influence de l'Alimentation et de l'Humidité sur la Variation des Papillons." By Arnold Pictet. (Mémoires de la Société de Physique et d'Histoire naturelle de Genève, vol. xxxv., fascicule 1, June, 1905, pp. 46-127.)

Among the principal conclusions arrived at by M. Pictet are the following:-(1) Change of ancestral food plant is often a factor of variability. (2) In general, a food difficult to absorb and digest prevents the larva from developing within its usual period, and this longer larval period is associated with the shortening of the pupal period, and consequently with insufficient pigmentation. (3) Normal food plant in insufficient quantity has the same effects. (4) A food easy to take in (ingérer) and rich in nutritious elements accelerates the larval development, and thus reacts on the duration of the pupal period, which being thus lengthened, a more intense pigmentation