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brings all the main facts to a focus, sifting and sorting them and ultimately deriving the final results. In the following few brief extracts we propose to give in the author's own words some of the more important conclusions to which the examination of the facts has led him, and we will commence with the ruddy appearance that the planet puts on, the cause of which has always been and still is doubtful. Apropos of the suggestion that there may be red and not necessarily green vegetation on the surface of Mars, he says—

“Pourquoi, dira-t-on, la végétation de Mars ne seraitelle pas verte?"

"Pourquoi le serait-elle ? répondrons-nous. La terre ne peut pas être considérée à aucun point de vue, comme le type de l'univers.”

"D'ailleurs, la végétation terrestre pourrait être rougeâtre elle-même, et elle l'a été en majorité pendant bien des siècles, les premiers végétaux terrestres ayant été des lycopodes, dont la couleur est d'un jaune roux tout martien. La substance verte que donne aux végétaux leur coloration, la chlorophylle, est composée de deux éléments, l'un vert, l'autre jaune. Ces deux éléments peuvent être séparés par des procédés chimiques. Il est donc parfaitement scientifique d'admettre que, dans des conditions différentes des conditions terrestres, la chlorophylle jaune puisse seule exister, ou dominer. Sur la terre, la proportion est de 1 pour 100. Ce peut être le contraire sur Mars."

In a most interesting chapter comparing the Martial with the terrestrial seasons, many important points of

similarity and difference are indicated. While the seasons

of Mars are of nearly the same intensity as ours, yet the respective "working powers," so to speak, last nearly twice as long. The cold and hot seasons in the northern hemisphere continues for 381 and 306 days respectively, and it is this fact which explains the great difference between the two hemispheres. The polar caps, as with us, vary with the seasons, but attain their maxima and minima three to six months after the winter and summer solstices respectively. The dimensions which they assume cover in winter 45° to 50° in diameter, and become reduced in summer to 4 or 5°. Just outside the polar regions, “des chutes de neige ont été observées dans les régions tempérées, et parfois même jusqu'à l'équateur. On a vu dans l'hémisphère boréal des traînées en spiral venant du pôle, indiquant des courants atmosphériques influencés par le mouvement de rotation de la planète. La calotte polaire boréale paraît centrée sur le pôle. L'Australe en est éloignée à 5°, 4 ou 340 kilomètres, à la longitude 30°, de sorte qu'aux époques de minimum le pôle sud est entièrement découvert: la mer polaire est libre." That actual changes have taken place on the planet's surface, in spite of the numerous sources of errors to which such delicate observations are liable, seems to have been proved by the discussion of the material. In speaking of these sources of errors he says, "Ces diverses causes de variations apparentes dans les aspects des configurations géographiques de Mars suffisent-elles pour rendre compte de toutes les variations observées ?" "Non."

“Des changements réels ont lieu à la surface de la planète, changements qui n'ont rien d'analogue dans ce qui passe à la surface de la terre."... "Nous voulons parler de celle de l'étendue des taches sombres regardées comme mers, lacs ou cours d'eau.”

The channels, the origin of which has been productive of so many hypotheses, are, according to the author, “dus à des fissures superficielles produites par les forces géologiques ou peut-être même à la rectification des anciens fleuves, par les habitants, ayant pour but la répartition général des eaux à la surface des continents. With regard to their doubling, after an examination of several hypotheses, he is led to look upon this fact as the result of refraction, although he remarks that "notre savoir est insuffisant," and "le connu n'est qu'une île minuscule au sein de l'océan de l'inconnu." He says, "Quant aux dédoublements, il est difficile d'admettre que réellement de nouveaux canaux se forment du jour au lendemain, semblables et parallèles aux premiers: nous préférons imaginer qu'ils puissent être dus soit aux brumes dont nous avons parlé, soit plutôt à une double réfraction tions de température (la chaleur solaire traversant faciledans l'atmosphère martienne. Etant données les condiment l'atmosphère martienne pour échauffer le sol, l'évaporation doit être très intense, et il doit y avoir constamment, au-dessus de ces cours d'eau, une grande quantité de vapeur rapidement refroidie, qui peut donne: naissance à des phénomènes de réfraction spéciaux."

In the concluding chapter, giving us a résumé ot the conditions of life at the planet's surface, the author sums up some of the main results. The world of Mars

“paraît être, comme le remarquait déjà William Hersche.. de toutes les planètes de notre système solaire, celle qui ressemble le plus à la nôtre. Nous pouvons répéter aujourd'hui, sur les habitants de Mars, ce que ce grand observateur écrivait, il-y-a plus d'un siècle, le 1er Décembre 1783: ‘its inhabitants probably enjoy a situation in many respects similar to ours."" It is possible, he adds, tha! this world may be peopled with beings analogous to our own: a race superior and in a more advanced stage, for the globe of Mars, M. Flammarion holds, is an older member of the solar system than our own.

Such, then, is a general sketch of the contents of this handsome volume of 600 pages. A glance through it is sufficient to show that no pains have been spared either by the writer or by the publisher, which might in any way add to its completeness; while the illustrations, which in such a work as this are of the highest importance, have been scattered with a lavish hand, and with all due regard to accuracy and purpose, no less than 580 telescopic drawings and 23 maps appearing.

In such a collection of facts as we have here, only ore slight erratum has been observed, and this occurs on page 287, where it is stated that M. (now Prof.) Schur, at the observatory of Breslau made some measurements of the planet's diameter, while it should have been, “ a: Strassburg with a Breslau heliometer."

Throughout the work M. Flammarion has in every case given full references, which greatly enhances its vale while in the appendix several drawings made during the opposition of 1892 are inserted.

Never before was the planet viewed with such keenness by astronomers as was the case last year, and it is by these. as well as by those that have never had such an opportunity, that this work will be found of absorbing interest. astronomical literature is considerably enriched by appearance.

WILLIAM J. S. LOCKYER

MAGNETIC OBSERVATIONS IN THE

NORTH SEA.

Magnetische Beobachtungen auf der Nordsee angestellt in den Jahren 1884 bis 1886, 1890 und 1891. Von A. Schück. (Hamburg: Selbstverlag des Verfassers, 1893-)

THE

HE extended and valuable magnetic surveysnotably those of Rücker and Thorpe in England, and of Moureaux in France-which have been made during the last ten or fifteen years, have provided magneticians with considerable information as to the conditions of the earth's magnetism in the countries bordering on the North Sea. From such data, there should be no difficulty in calculating normal curves of the three magnetic elements for the comparatively small intervening region covered by that sea.

The surveys on land have, moreover, shown that there are several regions of local magnetic disturbance, and therefore the chief interest of a magnetic survey of the North Sea, would lie in the discovery from observation on board ship, whether local magnetic disturbance existed in the land under the sea. The settlement of such a point would be a valuable contribution to our knowledge of terrestrial magnetism, and certainly if large disturbance were observed in any locality, of great practical importance to navigation.

Captain A. Schück has, for some years, past been making observations of the three magnetic elements with a special set of instruments well designed for observations at sea. Great pains have been taken by him to eliminate all sources of instrumental error, and he selected those wooden ships which appeared to him so far free from iron in their construction, that his magnetic instruments when mounted on board would be undisturbed. The results of his four years' work are given in the text with full descriptions, and illustrated by drawings of the instruments, as well as a chart of curves of equal value for each magnetic element.

The execution of these charts leaves much to be desired, for the figures on the land are in many places so crowded together as to be almost illegible, and it would have been much more to the purpose, if the lines of equal values had been at once taken from the published maps of the several observers, whose work the author fully acknowledges, instead of crowding together the data. upon which their lines are based. Again, the curves for those regions covered by the sea are in places so abnormal that they invite inquiry as to the accuracy of the small number of observations upon which they in many parts depend.

Although the author gives general assurances as to the selected ships being free from any source of magnetic disturbance, there are really no results recorded, to show that the observations at sea were really free from the effects of iron in the several vessels on board which the magnetic instruments were used. Long experience shows, that unless specially built, no wood-built ship is so far free from iron that its action can be neglected, especially when minutes of arc in an observation are of importance. If observations at sea over so small an area as the North Sea, and the channels south and west of Great Britain, are to effectually supplement those extensive

magnetic surveys made on the countries adjacent thereto, they must be stripped of every source of error. It does not appear that the observations recorded in this work are of the exact order suitable to modern requirements, however useful they might have been many years ago.

A work like that undertaken by the author, requires a specially-constructed vessel, devoted for the time to magnetic observations and other subjects of scientific inquiry. His objects were evidently delayed in execution by insufficient means to a satisfactory end.

MANUAL OF DAIRY WORK.

Manual of Dairy Work. By James Muir, M.R A.C., Professor of Agriculture in the Yorkshire College, Leeds. 93 pp. (London: Macmillan and Co., 1893.) HIS small primer on dairy work is in several respects

THIS

a contrast to some of the books and pamphlets relating to dairy matters which have appeared within the last two or three years. Many of these have had too many points in common with a dairy utensil manufacturer's catalogue, and the information they contain has not always been either condensed or trustworthy. It is therefore a pleasure to take up Prof. Muir's little manual, which gives in small compass a great deal of information likely to be of value to every one interested in the production and use of milk. Apparently the book is intended for those who, having practical knowledge of the management of milk and its products, desire further knowledge of the principles upon which their practice is based, together with hints as to the best means of utilising their commodity according to the demands of their own particular market.

The information given is in most cases well up to date, but at the same time the discussion of obscure matters connected with the bacteriology of milk is carefully avoided.

This is the more to be commended because every teacher of agriculture must know that looseness in describing the work of micro-organisms producing decay, or nitrification, or fixation of free nitrogen, has in many cases caused utter confusion in the minds of students; and more especially harmful is the imagination sometimes exercised by reporters and writers for the agricultural press. It is difficult to estimate the importance of Bacteriology in its relations to Agriculture and to Dairying, but in all discussion of the subject it is well to keep to ascertained and confirmed fact.

Prof. Muir's book is divided into ten chapters, the first of which deals with the formation and composition of milk. The description of the formation of milk in the udder is a trifle loose, the entire process being described as a casting off and breaking down of the cells which line the alveoli of the mammary glands. Milk is no doubt largely produced in this way, and especially must this be the case with colostrum when the glands commence or resume their activity; but it is more than probable that afterwards the milk is to some extent elaborated from the blood through the activity of the cells without so much actual shedding of the cells taking place. The great difference in composition between colostrum and normal milk shows that this latter process must be an important one.

In the third chapter some tests of the quality of milk are discussed. The value of milk is gauged by the percentage of butter-fat, and although there are many methods of estimating this, most of those which are trustworthy are troublesome to work. Prof Muir does not speak well of the lactobutyrometer-an instrument designed for the separation and direct reading of the fat. The method is certainly rough, and almost useless, except in the hands of a very careful worker. There are two methods, not described by Prof. Muir, which are of much greater value and not more troublesome; these are the Babcock milk test and Soxlet's method of estimating fat in milk from a determination of the specific gravity of an ether extract.

In speaking of cream separation on p. 45, Prof. Muir mentions that "some kinds of separator have an arrangement for regulating the thickness of the cream," and also "that frequently separated cream is rather frothy." A fuller treatment of these points would have been useful. The methods of regulating thickness of cream from a separator depend upon varying the rate of revolution of the separator bowl, or else upon varying the time the milk remains in the bowl. The latter plan is most convenient, and is usually effected by diminishing the inflow of milk In the Danish separator the same end may be secured by adjusting the movable skimming tube. Frothiness of cream is most marked in the case of the Danish machine when the cream is taken off thick. This frothiness might possibly be remedied by using a smaller nozzle for the cream delivery tube.

In dealing with the principles of cheesemaking on p. 69, the author says, "The state of the milk with regard to acidity is of the greatest importance just when the rennet is added, and should it then be too acid little can afterwards be done to counteract the mistake. On the other hand, should the amount of acid be slightly too little, it may be counteracted to some extent in the subsequent processes."

As a matter of fact even the most skilful workers some

times find the milk too ripe, and in such cases, by hastening the curd into the curd-sink and then washing with water at 100 F., good results may be obtained, at least by the "stirred-curd process."

The book concludes with a short appendix on creamraising trials, made at the Yorkshire College.

Prof. Muir's manual, though small, is to be welcomed as a most useful addition to our dairy literature.

WALTER THORP.

OUR BOOK SHELF.

William Gilbert of Colchester, Physician of London, on the Loadstone and Magnetic Bodies, and on the Great Magnet the Earth. A New Physiology, Demonstrated with Many Arguments and Experiments. A Translation, by P. Fleury Mottelay. (London: B. Quaritch, 1893.)

AMONG men of science there is no difference of opinion. as to the value of the original Latin work, "De Magnete," of which this is a translation. Some time ago (NATURE, vol. xlii. p. 279) we gave an account of a meeting held at Colchester by members of the Essex Field Club and the Gilbert Club, for the purpose of doing honour to the memory of Gilbert, who was born there in 1540. In a speech delivered at this festival Lord Rayleigh not only

spoke highly of Gilbert's work, but went on to say that although we owe to an investigator who lived so long ago the theory that the earth is a great magnet, we are not touch in advance of that position at the present time, as nobis has yet explained the origin of terrestrial magnetism. was most desirable that a work which may be said to have marked a definite stage in the evolution of physica science should be presented in an English form, and this has now been done by an American scholar, who, as be himself explains, has "translated with latitude, keeping in view the author's sense more particularly than his words, and amplifying without altering the former." Mr. Mottelay has also brought together in a short biographi cal memoir the leading facts relating to Gilbert's career. The volume is well printed on good paper, and will be very welcome to students of the history of scientibu ideas.

Report on Manurial Trials. By Dr. Williar Somerville. (Newcastle: Ward, 1893.)

THIS pamphlet, extending to 61 pages, gives the results of manurial trials in the county of Northumberland during the season 1892.

The plan of the experiments is an extensive one, but we may say that many of the experiments are designed to show what manures can be economically applied in the growth of turnips and potatoes in ordinary rotation.

From the experiments made upon farms at Rothbury, Ilderton, Tweedmouth, and Wark-on-Tyne, Dr. Somerville concludes that (1) basic slag is the cheapes phosphatic manure, though the best result is obtained with a mixture of slag and superphosphate; (2) kant up to 2 cwt. per acre is a profitable dressing to turnips and potatoes; (3) the turnip crop requires nitrogenous manure; and (4) small dressings of artificial manures are more directly profitable than large dressings.

It is to be hoped than many of these experiments will be repeated in the county this year. W. T.

The Food of Plants. By A. P. Laurie, M.A., B Sc. (London: Macmillan Co., 1893.)

THIS little book is intended to be an introduction to agricultural chemistry. It contains descriptions of a series of simple experiments which may be undertaken without any previous knowledge of chemistry. These experiments illustrate the part played by water in the nutrition of plants, the nature of the soil and of the air, and how plants obtain their food from these sources, &c.

The experiments are carefully chosen and described, and can be performed with inexpensive materials, and the book, especially if used as the author suggests, in conjunction with a Chemistry Primer, can well be recommended as an interesting guide to the study of agriculture.

LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinions ex pressed 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.]

Fossil Floras and Climate.

I HAVE read with some interest the communications in recent numbers of NATURE based on a review by my friend Mr. Starkie Gardner of a book which I have not yet seen; and as an exile in the south owing to a serious illness, I have not means of reference even to my own papers on the topic in discussion. I think, however, it may be well to direct attention to some Canadian fac's published in the Transactions of our Royal Society and elsewhere, to which neither Mr. Gardner nor Mr. De Rance have referred.1

1 See Report of Dr. G. M. Dawson on the 45th Parallel 1875; Reports Geol. Survey of Canada, 1871-'77-79; Transactions Royal Society of Canada 188; to 1892.

In Western Canada, in the Rocky Mountains, and in the Queen Charlotte Islands (latitude 55°) we have a lower cretaceous flora, characteristically mesozoic, and even allied to the urassic. Two of its characteristic species are closely allied to Divon eduli of Mexico (Divonites Columbianus and D. borealis, Dawson). Along with these are species of Zamites and of Podozamites, and leaves of Salisburya, very near to those described by Heer from the so-called jurassic of Siberia. The owest beds of this series contain no angiosperms; but in beds little higher these begin to occur. This has been named in Canada the Kootanie flora, from the river of that name in the Rockies. The late Dr. Newberry, in one of his latest papers, described the same flora with identical species as occurring in Montana, and it coincides in part with the Potomac flora of Fontaine in the south-eastern states. Its character and disribution show an extension of warm climate from Florida to the Queen Charlotte Islands, coincident with a great northward extension of the warm waters of the Gulf of Mexico, which in my judgment is sufficient to account for the climatal conditions. This lower cretaceous flora may be considered to be Neocomian in age, and to correspond with the Wealden of England, and the Komé of Heer in Greenland, which shows the extension of at least a temperate climate beyond the latitude of 60o.

The middle cretaceous brought in a still greater extension of the warm Mediterranean Sea of interior North America, indicated by the chalky foraminiferal Niobrara beds of the United States geologists, which extend into Canada. North of these marine beds, however, we have in Canada, in N. lat. 55°, the Dunvegan sandstones and shales, which hold not only cycadaceous plants but a rich angiospermous flora, including such warm temperate genera as Magnolia and Laurus, with more northern forms as Betula and Populus. This we regard as a middle cretaceous flora, in its older part approaching the wellknown Dakota flora of the United States, and corresponding to the Atané of Heer in Greenland. The climate in this period must have been humid, equable, and temperate, all around the great American Mediterranean; but it is not impossible that our Dunvegan collections may include some plants of mountain districts mixed with those of lower grounds.

This was succeeded by the upper cretaceous, in the older part of which we have the magnificent flora of the coal series of Vancouver Island, which represents a Pacific coast flora, with fan palms, live oaks, and other trees comparable with those of modern Georgia and Florida. By this time, however, there would seem to have been a geographical separation between the Pacific coast and the plains, as the latter have not yet afforded anything equivalent to the Vancouver flora, and there are some indications that, toward the close of the cretaceous, the climate was cooler than previously. This is equivalent to the Patoot series of Heer in Greenland.

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The Laramie period proper, that of the lignite tertiary for mations of the plains, seems to indicate a swampy and lacustrice condition of the interior plateau, and the rich angiospermous and gymnospermous flora of this time, characterised very markedly by species of Platanus and Sequoia, has a temperate aspect in Canada, as far north as the McKenzie river. responds with the so-called miocene of Heer in Greenland, but is shown by stratigraphy and by its affinity with the eocene of England and Scotland, as described by Mr. Starkie Gardner, to be of that age if not constituting a transition group between the cretaceous and tertiary. The paleobotanists of the United States, at first, following Heer, regarded this flora as miocene. More recently some are disposed to consider it upper cretaceous. In Canada it has all along been regarded as paleocene or eocene, and so far as its flora is concerned this is its true position. In a recent number of NATURE I see that Prof. Osborn is disposed to regard the small mammalia of the Laramie of the United States as of eocene affinities. If so, they will agree with the plants. It seems more difficult to account for the great northward extension of the Laramie temperate climate than for that of the preceding cretaceous, as the great Mediterranean of the latter seems to have dried up, though still existing in part, or replaced by swamps and lakes. Possibly some other arrangement of the warm Atlantic currents, as suggested by Mr. Starkie Gardner, may have produced some effect, in conjunction with obstruction of the Arctic currents, and a lower level of Greenland.

The general bearing of these facts on American climate is that we have no evidence of a tropical climate in Northern Canada

or Greenland, but that both the geographical and botanical facts indicate a warm temperate climate, at least in the cretaceous period, and that in the earlier eocene the climate was becoming cooler and less equable.

We have little to show for the miocene; but what there is, as in the Similkameen flora of British Columbia, would go to show a cooler climate and more of local variation.

I have little faith in attempts to deduce a mean temperature in degrees of Fahrenheit from fossil plants; but if carefully collected, so as to keep separate those that belong to different horizons, and if studied in strict relation to the geological conditions of their occurrence, they must afford excellent general indications of climate. Allowance must, however, be made just as in the case of animal fossils, for differences of station, altitude, &c., and for extent of probable driftage or occurrence in situ.1 In studying large collections of our mesozoic and tertiary fossil plants, from different localities and horizons, I have as a geologist naturally had reference to these points, and the work of such men as Selwyn, Richardson, G. M. Dawson, and Mr. Connell has left nothing to be desired as to careful collecting and determination of stratigraphical relations, while the study of animal fossils by Mr. Whiteaves has gone on pari passu and in harmony with that of the plants.

I sympathise with Mr. De Rance in his defence of Heer's studies of the Greenland plants, for I know that my own work in Canada would be liable to still more severe criticism. It must be borne in mind that the palæobotanist bas very imperfect material, and that he is always liable unconsciously to multiply species. If, however, his names serve to designate the things, and if their geological relations are known, an important work has been accomplished-always, however, provisional and liable to correction as new discoveries are made. One of my Kootanie leaves is scarcely distinguishable on the one hand from Heer's Salisburya sibirica, and on the other from Lindley's Cyclopteris digitata, even when I have specimens of both to compare it with. All may be the same, though referred on the one hand to ferns, on the other to coniferæ, and this may not be settled till specimens in fruit are found. in any case something has been done, and a widely distributed vegetable form has been recognised at a particular stage of the world's history.

But

I hope to discuss some of these points more fully in a work now in the press. WM. DAWSON.

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Augusta, Georgia, March 13. P.S.--Since writing the above I have obtained access to a copy of Dall and Harris's "Neozoic Correlation Papers,' which throws some additional light on the cretaceous and eocene floras of Alaska, which, from its high northern latitude, affords a good term of comparison with Greenland. It would appear that fossil plants occur at two horizons. One of these (Cape Beaufort), according to Lesquereux and Ward, holds species of Neocomian age, equivalent to the Kootanie of British Columbia and to the Komé of Greenland. The other, which occurs at several localities (Elukak, Port Graham, &c.), has a flora evidently of Laramie (eocene) age, and equivalent to the "mioof Heer and Lesquereux and to the McKenzie river and lignite tertiary of Canada. The plants are accompanied by lignite, and evidently in situ, and clearly prove harmony with Greenland and Northern Canada in two of those periods of high Arctic temperature indicated above.

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Notes on a Spider.

I SEND you the following notes on a spider, whose curious habits I had an opportunity of observing, last year, on the West Coast of Africa:

In the month of August, 1892, I was travelling by hammock from Chama to Sekundi, two small towns on the Gold Coast. That part of the country is somewhat hilly and is covered with "bush and other forest growth. The road skirts the sea-shore, sometimes following the beach itself, at other times taking turns inland and winding round bases of small hills.

It was about three in the afternoon and I was being leisurely carried along by my bearers, when I noticed in the bushes that bordered the path something which appeared to me to be a sort of white flower.

1 Ward, of the U.S. Geol. Survey, has directed attention to these points in an excellent paper published by the Survey. 2 Bulletin U.S. Geol. Survey, 1892.

I stopped and examined it. Instead of being a flower, I found it was the web of a spider, and it was hanging between the branches of a shrub about three feet from the ground. The outer lines of the web were of considerable strength and were stretched between points from eight to ten inches apart. From these lines, supported by a few radii, hung a beautiful rosette-shaped centre, much resembling a delicate pattern in white silk lace. The central space was open and measured about a quarter of an inch in diameter. The notched space was adorned by three circular zig-zag cords of thick white flossy silk. I did not notice any of MacCook's so-called "ribbon braces." The spiral space was very open and the threads composing it were so slight as to be almost invisible. So thin were they that the ribboned centre appeared to be hanging in the air without any support whatever. The appearance of this web was almost exactly similar to that of the web of Uloborus, shown in Fig. 57, p. 58 of MacCook's "American Spiders." I did not notice any "fenders" or protective wings on the outer side of the web; there were, however, a few strengthening strands on the side turned towards the bush.

The web, however, especially bore a strong resemblance to a flower, the more so as in the exact centre of its outward side was stationed a spider with a light blue body. This light blue colour gave one the impression that it was the centre of the flower, while the yellow legs spotted with brown were symmetrically disposed in the shape of an X across the ribboned hub, thus dividing it into the semblance of petals. The illusion was remarkable.

The spider remained motionless until I touched the web. She then fell into the net which I was holding under the snare.

As soon as she touched the net a white gauze one) she changed colour. From blue she became white and then, on being shaken, her body turned a dark greenish brown. I then placed her in a glass tube and gradually she resumed her blue tint. Whenever shaken, however, she turned a greenish brown. I placed her in spirits and her colour remained a grey brown.

On the same road later in the day, I noticed another strange web which bore even a stronger resemblance to a flower.

The foundation space was the same as in the other, but somewhat larger and stronger. The white silk ribbon, however, instead of being disposed around the centre in circular zig-zag lines, was extended in two thick white ribbons stretched crosswise along four of the radii. In this instance also the spiral space was very open and the spirals very delicate.

The spider inhabiting this web was considerably larger than the foregoing specimen, but appeared to be otherwise exactly similar to it. Her body was a very light blue, placed exactly in the centre of the cross, head downwards, while her long legs were disposed in pairs over the four arms of the white silk pattern. The whole thing bore a great resemblance to an orchid, and the legs of the spider gave it just sufficient stability for it to be taken for a flower.

When I touched the web the spider immediately darted through two strands in the spiral space and placed herself on the reverse side of her web, being almost completely concealed by the thick flossy white ribbons.

I captured this spider, and her body, like the other specimen's, immediately turned a dark greenish brown. I did not, however, see her turn white. I placed the insect in a glass tube, and five days later put her in a cage.

I also took the web and succeeded in fastening the centre of it on to a black card, where it remains in exactly the same shape as when it was hanging on the bushes. I have this web, and also a photograph of it.

The day alter the spider was placed in the cage she made a web. It was spun during the night, and I did not observe the operation. The web was of the same pattern as the one on which I discovered her on the bush. It did not have any circular zig-zag cords.

This spider remained in her cage for four or five weeks, and then I placed her in spirits. She was fed principally with flies.

On one occasion I pat a very large blie-bottle fly into the cage. The spuier seizei it ime lately, violently vibrated her web, and at the same time rolled the fly round and round between her legs. In the space of three or four seconds the fly was completely swathed in an envelope of white silk, and was motionless. The spider then fastened her fang, into the body, and sacked it for about two hours,

I have since seen several of these spiders on their webs, and have abtices that the pattern of the saire appears to lepeil sa

the size of the insect, the smaller specimens making the cir cular rosette shaped snare, while the larger insects weave the cross orchid-like flower. I saw one small web composed of tw little rosettes, joined side by side, but I did not notice wherber it was inhabited by two spiders. I frequently found wings and other debris of insects hanging to the rosettes of the webs, an in one case saw a wing of what must have been a butterly of considerable size.

When does the spider alter the pattern of ber snare? Cat i be that, when the spider attains to full growth, finding that the rosette shape, becoming too large, no longer deceives butterflies and other insects, she adopts the orchid-like pattern wh has more vraisemblance, and over which she can dispose ba long legs with a better chance of successful trickery.

The web of this spider being so like a flower would appear to be intended as a veritable "snare." The insect by assumin its bright blue colour increases the resemblance and the mimicry is probably practised not so much for the protection of the spude herself, but rather for the attraction it presents to butterflies and other flower frequenting insects.

MacCook in American Spiders," writing of the mimicry a spiders, and of their perception of colour, says (vol. ii, p. 346, :— "There is indeed another theory which may be suggeste namely, that the colour surroundings of the spider, in some manner not now explicable, so rapidly influence the organism í the creature that a change of colour is produced in harmony wa its environment. Can we suppose in this case that the spide possesses the power to influence at will the chromatophores or p ment bodies, so that she may change her colour with chang site?"

The specimen observed by me would seem to be an answer": MacCook's suggestion, and I should be very glad to know, through the medium of NATURE, or otherwise, whether the spider described by me, as above, is already known naturalists.

I took the specimens which I possess to the Natural History Museum, at South Kensington, and the spiders were declared be a species of Argiope.

H. H. J. BELL,

Senior Assistant Treasurer, Gold Coast Colony. 20, Sussex Villas, Kensington, W.

Origin of Lake Basins.

ONE of the chief reasons for the prevalence of lake basin. have recently appeared in NATURE on the origin of lake bastre in glaciated countries has not been alluded to in the letters which

Whenever earth movements take place in limited areas suc movements will tend to form basins, but as the movements ar as a rule gradual such basins will only come into existence unter exceptional conditions. Water-borne detritus, the growth vegetation, and erosion will obliterate them in most cases as fast as they are formed by slow unequal movements of suns.dence a elevation.

tion by unequal earth movements will be largely protectes from In glaciated countries, however, basins in the course of forma such destructive action by being filled with ice, and will thas le

preserved to appear as lake basins when the ice meits.

So, too, in countries where the rainfall is very small ani .he action of the forces destructive to lake basins is according i mach diminished basins may be and are formed by eart movements. In rainless countries they are probably micr numerous than we are aware of, for there is little to attrac attention to them, but they will become of more importance is works of irrigation_are_required in such countries. portant depression, the Ruin basin, has lately been surveyet in Egypt by Mr. Cope Whitehouse with a view to utilising for irrigation purposes Proceeding Royal Geographical Society, 2nd series, vol. ix. p. 603.

Wind-borne detritus will tend to diminish the depths such basins in rattless countries. So, too, the capiety o ice-filled basins to hold water in the future will be diminishe somewhat by the erosion of the sub-glacial river, but on in other hand as the movement of the earth deepens the basin 'he ever-tuickening mass of ice will acquire increased power to grind it deeper stil. This grinding action cannot be ignored. and some shallow lake basins may be almost entirely ae t it, but there is scarcely a limit to the formation of such bases by earth movements under suitable conditions.

J. C. HAWKSHAW

33, Great George Street, Westminster, S. W., March 29.

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