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emake explicit use of the Principle of the Permanof Equivalent Forms, which, after having been exded at length and defended by Peacock (appendix algebra"), has been summarily rejected as misleading anmeaning by many recent authors. To the formal roduction of this principle Mr. Hayward's language its a tendency to return. Outside the domain of entary Algebra, its strict employment in the prolonn of an analytical function into a new region is d of common occurrence in Analysis; while its tenapplication in unrestricted form, as an instrument ggestion and discovery in the Theory of Operations, ndamental. To the effort to widen the limits of pretation in connexion with it, has been due most of dvances in Analysis.

$ a fundamental question in mathematical logic how fter having carried the stream of our analysis through ns of uninterpreted symbols, and having at length ed at a stage in which these symbols have disaped, we are entitled to claim this procedure to be nstrative. It is of course of the very essence of ora that the intermediate steps of its analysis remain erpreted; though in the Algebra of real quantities we a tacit assurance that an interpretation can be supif necessary. Why then was there an objection imilar procedure in the Algebra of complex quantiand what is the source of the timidity and doubt characterized the use of complex analysis before cometrical interpretation was developed? Simply complex quantities turned out to be multiple-valued, hat the selection of the proper value under given nstances had to be settled by tracing the continuity quantities in a way that was to the mind practically ssible until a visual geometric representation was vered. The Argand diagram is not essential to the of the matter; it rather makes Analysis possible by ing its scope within our grasp. It simply forms a extensive and systematic example of the method 1 has been in use since the time of Descartes for ing functions and approximating to their roots, by f their graphical representation.

e Principle of Permanence of Equivalent Forms thus t the very root of Algebra, but it is rendered ineffective determinateness of interpretation. Its strict use, most needed, is subject also to another hitch. It es that the forms be expressed in exact terms; an e series must be expressed in the sum of n terms her with a residue R. These residues must be ed throughout the analysis until we arrive at a point interpretation comes in; and it must then be how far they can be neglected in the circumstances = actual interpretation. In the language of Mr. ard, it cannot be asserted about series that are not ately convergent, that the fundamental laws of ra hold without limitation.

= perhaps a question how far the idea, thus restricted feguarded, is worth being expressly retained as a ng principle of ordinary Algebra. In subjects like lculus of Operations and Finite Differences, which 11 in an unsytematized stage, it cannot be dispensed and the extent to which its use is boldly pushed, Morgan and Boole, even to the discussion in an onal manner of divergent series without their

residues, contrasts with the more exact processes of recent Analysis. How far this boldness arises from the profound logical studies of these writers, and their appreciation of the imperfect character of inference at the best, may be a subject open to discussion.

In connexion with the doctrine of convergence of series, the author gives a very clear account, from Sir G. Stokes, of how it is that, on approaching certain critical points, the convergence may gradually fall off and finally disappear. The illustrations employed are algebraic series of an exceptional character; and the whole circumstances may possibly suggest to the uninitiated that it is a phenomenon of exceptional rarity. The most natural context is, of course, in connexion with the wonderful and far-reaching theory initiated by Fourier, by means of which functions arbitrarily discontinuous are expressed by seemingly continuous series. In that connexion, the necessity of explanation is so obvious that it is interesting to examine the previous attempts at elucidation. Thus De Morgan, in 1839, is able to conclude ("Diff. and Int. Calc.," pp. 233, 239) that such discontinuity cannot occur in series proceeding by powers of a real variable; that in other cases it occurs only through the series becoming divergent at the point of discontinuity. It is, however, an important question how far it would be allowable to avoid burdening an elementary exposition by complete precautions against the existence of anomalies like this, which would hardly have originally occurred to any one in that early stage.

The book ends with a wider survey, including a clear and interesting account of Cauchy's theory of the radical points of a rational function. The graphs of the cubic 3+ az, which are given as an illustration, would also form excellent and rapid examples of the Rankine-Maxwell method of graphical addition, applied to the separate graphs of 3 and az.

J. L.

FOSSIL PLANTS AS TESTS OF CLIMATE. Fossil Plants as Tests of Climate, being the Sedgwick Prize Essay for the Year 1892. By A. C. Seward, M.A., F.G.S., Lecturer in Botany in the University of Cambridge. (London: C. J. Clay and Sons, Cambridge University Press, 1892.)


'HIS admirable essay is really a digest of the opinions of the principal writers on fossil plants, so far as they throw light on geological climates, and a critical résumé of the subject up to date. It should be read by all who prefer to deduce the relative temperatures of various latitudes in the past from such solid data as assemblages of ferns, cycads, and conifers, the ancestors of living genera and species, rather than from utterly extinct belemnites, ammonites, and saurians, of whose habits little can ever be known, and which might have drifted far out of their temperature zones by warm and cold sea-currents.

Perhaps if any criticism can be made, it is that too little has been said by the author as to what is known of the Mesozoic floras, which, if scanty, are extremely interesting. In fact only the widely-separated Palæozoic and Cenozoic floras are fully dealt with. Owing to the magnitude, difficulty, and freshness

of the problems presented by the former, they have received the larger share of attention and have ever attracted some of the most acute and philosophic of scientific workers. But while the researches of such investigators as Williamson and Renault into the actual structures and affinities of the carboniferous plants have been rewarded with the most brilliant successes, attempts to speculate and theorize have only been productive of barren controversy. All inferences as to the temperatures in which they flourished have merely been inductions from unknown data: their affinities with existing plants are so remote that they can tell us of little beyond moist climates and spongy, marshy soils, liable to inundation, with possibly an atmosphere more highly charged with carbonic acid than at present. But that neither the flora nor identical conditions were uniformly present over the whole land during the deposition of the carboniferous, becomes every year more apparent; and perhaps few would now maintain that fossil floras met with in widelydifferent latitudes must necessarily be contemporary because similar, or reject as impossible the correlation of the Glossopteris floras of the southern hemisphere simply because they are so dissimilar.

Tertiary floras, however, have to be approached from almost totally different standpoints, for here minute investigations into vegetable structure can only exceptionally lead to important results. On the other hand it may be possible to predicate the climate that any group among them would have required, with almost perfect accuracy. Allowing that even most closely-allied species may have had different habits, enough remain that are practically identical with living species. These not only prove to us that in every land in our hemisphere the temperatures remained warmer throughout the Tertiary period than at present, but also that the temperatures were far from equable during Eocene time. Thus it is impossible to hesitate as to the evidence of the flora in the lower stages of our Eocene, which exhibits an abundance of planes, poplars, and alders and an absence of all approach to sub-tropical essences; nor as to that of the London Clay, with its tropical nipas, sabals, and a host of others almost indistinguishable from species existing at the present day. There is scarcely need of the corroborative evidence of the Mollusca as to cooler seas in the Thanets, nor of tropical conditions in the large turtles, crocodiles, snakes, and nautili of Sheppey. In fact, the temperature of the spots occupied by Reading, Bournemouth, or Mull at a particular stage of the Eocene could be predicated from the fossil floras almost as accurately as from living plants. If the same cannot be said of the Arctic regions it is simply that the specimens brought home are, perhaps from the exigences of travel and inexperience of the collectors, for the most part so imperfectly preserved and fragmentary, that few of the determinations can carry the smallest weight. It may suit quidnuncs to accept indeterminable fragments as evidence of the growth of palms and cycads in the Greenland Eocene-it is time the Miocene age of these beds was relegated to the limbo of Coal-measure palms and yuccas-and to become excited over the presence of a sub-tropical flora within the Arctic circle; but as a fact it is doubtful whether anything has been discovered there which might not have grown in our own temperature, if

slightly modified, a state of things which it the damming back of the Arctic seas by the tion which then existed between Europe ! aided by an active Gulf Stream, might re about. When we come to the Miocene, wat that of Switzerland was by Heer, or E. Quaternary, with such data as those laboro. by Clement Reid, the inferences as to dine more irresistible.

As to evidence of the age of rocks, plants are worthy, because they have neither been studied nor are their zones as yet at all proper All we can say is that certain assemblage z in association at the beginning of the Ter that changing temperatures have since compel not to disperse, but to migrate far and wide .. bably of the species are extinct than is generall and the primitive associations have held toge::e to the present day, with many gaps from extr desertion and a large infusion of recruits th ordinary causes of evolution, stimulated by the r browsing mammalia. Whether, on the other marine deposit zones are really entitled to the tached to them as evidences of age, except loca clear. They are usually the littoral deposits .. area, where some changes of level or current ently suddenly driven out the fauna and intro. colonies more adapted to the changed conditi could follow the subsequent wanderings of the blages under the sea our faith in their sudden e and consequently in their chronological value greatly modified. At all events, many of the las spicuous groups of mollusca, when critically evi prove to have surprisingly near relatives in disz at much later periods, and even at the present d J. STARKIE GAR

OUR BOOK SHELF. Pioneers of Science. By Oliver Lodge, F.R.S. and New York: Macmillan and Co., 1893) THIS book consists of eighteen lectures on the

and progress of astronomy, which were delivere Lodge in 1887. "The lectures having beet interesting," he thought it "natural to write the full and publish," and, although this can scarcely to sidered a sufficient excuse, the intrinsic men work are abundant justification for its exister : Part I., "From Dusk to Daylight," the pro astronomy from Copernicus to Newton is trace series of vivid pictures of Copernicus, Tyca Kepler, Galileo, Descartes, and Newton; while "A Couple of Centuries' Progress," brings the of gravitational astronomy from Newton dow present time. In these latter lectures Roese Bradley are associated with the velocity of b aberration; Legrange and Laplace with the solar and the nebular hypothesis; Herschel with the of "fixed" stars; Bessel with the distances of Adams and Leverrier with the discovery of c and Lord Kelvin and George H. Darwin with totes Lodge has been able, by judiciously combia.rg statements of scientific facts and laws with inter personal details, to give his lectures all the chat romance. The book is an admirable introductio study of astronomy, and no better gift for 2, could well be chosen ; while to those to whom

tails are already familiar, the picturesque clearness hich they are presented will make their knowledge real and more complete. The standard of excelmaintained in the lectures makes distinction diffiad invidious, or we would distinguish the lectures wton and those on tides as models of what such ir scientific expositions should be. The book is isly, and, on the whole, well illustrated, but some of istrations-notably those of clusters and nebulæ ry familiar and somewhat out of date. A curious e occurs on page 201, where a well-known drawa comet appears as an old drawing of the Andronebula." The illustration on page 326, showing aths of Uranus and Neptune and their relative ns from 1781 to 1840, and professing" to illustrate rection of their mutual perturbing forces," is partly ding; but in introducing this Dr. Lodge has n good company, for the diagram, originally due to oughton, appears in many of our recent astronomical oks. A. T.


ic Lighting and Power Distribution. Part I. By Perren Maycock, M.I.E.E. (London: Whittaker Co., 1892.)

cheap and useful little text-book has been written : author's junior students, as he is of opinion that stworthy elementary work on the subject is to be ed. The scope of the work has been limited to Ilabus of the ordinary grade examination of the nd Guilds of London Institute. We find, however, information on subjects not usually found in other ls. The book is freely illustrated, and the deons are clear.

very important for the junior student to underclearly what is meant by a line of force, and to the fact that lines of force are only assumed to because, by such an assumption it is possible to 1 many, otherwise inexplicable, phenomena. On 7 we find the following statement :-"The power any magnet possesses, of picking up pieces of ind of acting upon another magnet, depends the existence of lines of magnetic force." This ion is vague; a junior student might easily e that the lines of force really existed, whereas tre purely assumptions, to elucidate the phenoof magnetic attraction. The illustrations of : bar magnets, solenoids, and electro-magnets, in the lines of force are delineated, should have the ed directions of the lines of force clearly shown by -heads. This might be done with advantage in

17 to 20.

pter IV. deals with induction of currents, electroetic induction, Faraday's Law, and concludes with r description of magneto-motive force, magnetic nce, magnetizing force, induction and permeability. latter are very difficult for a junior student to tand thoroughly, and the author should have d more space to the discussion of these important in dynamo construction. One particularly good in this text-book is the large number of questions ed at the end of each chapter. These are well to test the knowledge of a student. Chapter V. enerally with electrical testing, measuring instruused in installations, and meters for measuring rent, such as Teague's, Elihu Thomson's, and the t-Ferrauti. Chapter VI. concludes the book, deg the principle of the dynamo, different types of ies, and the construction of the various parts. en as a whole this book attempts too much. The described has suffered considerably by condensaserious thing where junior students are concerned. of the illustrations are good; some are indisand Fig. 98 is decidedly wrong, showing the brushes one direction of rotation, and the arrow indicating


On the other hand the sequence of matter is good, and a student should learn much from the work. The author takes great pains to describe clearly the many units involved, particularly the applications of Ohm's law. The book would last much longer in the hands of the average student if the present paper binding were replaced by something stronger.

The Naturalist on the River Amazons.
Walter Bates, F.R.S.
by Edward Clodd.

By Henry With a memoir of the author Reprint of the Unabridged With Map and Numerous Illustrations. (London: John Murray, 1892.)

THIS work is so well known, and has long held so high a place among scientific books of travel, that it is unnecessary to do more than note the appearance of a new edition. It is clearly printed on good paper, and the illustrations are well reproduced. The introductory memoir by Mr. Clodd is a most welcome record of the main facts of Mr. Bates's career. The materials for this author's disposal by Sir Joseph Hooker and Mr. Francis interesting sketch were enriched by letters placed at the Darwin. An excellent portrait of Mr. Bates is included in the volume.

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.]

A Proposed Handbook of the British Marine Fauna. SUCH a handbook as Prof. Herdman suggests is so much wanted that many naturalists must from time to time have felt tempted to essay it. But the difficulties are very formidable. Prof. Herdman seems to contemplate the preparation of such a work mainly as a labour of compilation. But the groups where compilation would nearly suffice are just those where the handbook is least required. On the other hand, such a group as the Amphipoda, in spite of Canon Norman and Mr. Stebbing's many papers, is still in great need of revision; it was only the other day that Canon Norman opened our eyes to our rich fauna of Myside, before which time no search among published records would have told us anything worth the having; we are in just the same position as to our British Cumacea, until Canon Norman again reveals the treasures of his cabinet; our Pycnogrns are almost as little known. In every one of these groups, and in the experience of a specialist, just as much as the Tunicata would many others like them, the preparation of a hand-list would need require Prof. Herdman's own special knowledge. The area to be embraced is another difficulty. Prof. Herdman proposes to take the British area as defined by "Canon Norman's " B. A. Committee in 1887, on which he himself served. But the committee's report was repudiated by Canon Norman himself, who afterwards suggested a wider "British area," whose boundaries I fancied had since been recognized as more suitable by everybody. However the British area be defined, there will long remain a difficulty in the numerous forms not yet recorded from within it, but which are likely, or certain, to turn up when sought for. of late years by Giard and his pupils from Wimereux form a Such things as the parasitic and other Crustacea described case in point. I am inclined to think that to make in the first instance a hand-list of the whole fauna of the North Atlantic basin would be not a bit more difficult, but in some respects easier, than to restrict the list to the British area alone. That it would be incomparably more useful is certain. It would make a book not more than three times (perhaps little more than twice) as big as Carus's "Fauna Mediterranea." And it would be a very important step towards that new systema nature of which the Germans are already beginning to talk, and which it is high time were begun.

But Prof. Herdman both asks discussion of his plan, and also invites criticism on his execution of it. Take his very first illustrative genus, which he tabulates as follows:

ANTENNULARIA.-Stems simple or branched; pinnæ verti cillate; nematophores along the stems; gonothecæ axillary, uni


A. antennina, L., stems clustered, usually simple; hydrothecæ separated by 2 joints. 6 to 9 in. high. Gen. distr. deep w. A. ramosa, Lamk., stems single, usually branched; hydrothecæ separated by 1 joint only. 6 to 9 in. high. Gen. distr. deep w.

Now there are no nematophores along the stem, but only on the pinnæ ; A. ramosa may sometimes grow up unbranched, but I for one never saw it so, and A. antennina is always simple, save by the rarest individual abnormality; the dimensions are quite inaccurate, for we have A. antennina here of all sizes up to 24 inches high. The distribution given is too vague. In the report of the B. A. Committee, which Prof. Herdman goes by, deep water is defined as that below 100 fathoms; but these two are not deep-water species, either in that or any other common use of the phrase. The authorities are very loosely given. A. antennina, L., should be (L.), and if the bracketed authority, i.e. the original user of the specific name, is to be the one quoted, then for A. ramosa, I think Lamk. should give place to (Lamx.). And why is the authority for the genus left out altogether?

Moreover, even if these definitions were verbally accurate so far as they go, they would only suffice to exclude one another, with no reference to other non-British species. They are rather definitions of groups of species or sub-genera, than of these two particular forms. It would not matter very much, perhaps, in this case, where other species are not likely to turn up upon our coasts; but such definitions, drawn with reference only to known British forms, would soon lead to hopeless confusion in the case of less-known groups. D'ARCY W. THOMPSON.

Dundee, January 11.

On an Abnormality in the Veins of the Rabbit. AMONGST a number of rabbits dissected in my laboratory last term, one specimen exhibited a peculiarity in the venous system which is especially interesting in connection with Hochstetter's and Macalister's accounts of the development of the veins. Unfortunately the specimen had been too far dissected before the abnormality was noticed to follow out every detail.

The blood from the hinder extremities, urinogenital organs, and abdominal walls, passed into a large vessel having the position and relations of a postcaval posteriorly. Instead, however, of passing through the dorsal border of the liver to penetrate the diaphragm, it was seen at the anterior part of the abdomen to correspond to the azygos, receiving the superior intercostal veins, and opening into the right precaval. This vessel evidently, then, corresponded to the persistent right posterior cardinal. The portal system was apparently normal, and the hepatic veins opened into a postcaval, which extended through the diaphragm to the heart in the usual manner.

Thus the independently-formed section of the postcaval (Leberabschnitt) had taken on no connection with the part developed from the cardinals (Urnierenabschnitt), but had remained as a separate vein, bringing back the blood from the alimentary organs (and ? diaphragm) only.

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I have not thought it necessary to do more than mention these facts, as the whole question has recently been fully discussed by Dr. A. Robinson ("Abnormalities of the Venous System and their relation to the Development of Veins," Studies in Anatomy from the Anatomical Department of the Owens College," vol. i. p. 197, Manchester, 1891). The above case, however, supports the view that the renal veins are direct tributaries of the right cardinal, and not of the postcaval; while the reverse conclusion is derived from Dr. Robinson's observations. W. N. PARKER,

University College, Cardiff, January 14.

Difficulties of Pliocene Geology.

You were good enough to print a letter from me a week or two ago, in which I called attention to some of the difficulties in explaining the distribution of the so-called Pliocene beds. I should like to prosecute the subject a little further.

The geographical distribution of the mastodon is assuredly one of the greatest paradoxes in natural science.

As is well known, it occurs both in North and South America, and on both sides of the Rocky Mountains and the Andes. It has not occurred, however, so far as I know, north of the great lakes in the east, nor of Oregon in the west, nor has it ever been reported from Alaska, where mammoth remains are so abundant. I do not know any evidence that it has been found anywhere in

Asia, north of the Himalayas, neither in China, a nor Mongolia, nor Turkestan, nor in Siberia, nor hasz in European Russia, except close to the Black Star nor in Scandinavia, nor in North Germany.

In the Old World its zone of distribation esteak to the Pyrenees, including the Mediterraneaa » valleys of the Danube, and the Middle Raine, La. land, and perhaps Iceland, whence some teeth are a been sent to the royal collection at Copenhagen. bution of a very highly specialized beast is certava v = ordinary. Granted that the mastodons of Wezen. 1 those of America are slightly different, the differet : that, as Falconer says, Cuvier treated them as the ram and they cannot have been very long isolated. let. to explain the facts, and do justice to the widespread the ocean areas are very old?

It seems to me as clear as anything can be it. « mastodon was distributed over Western Europe as. there must have been a land communication bever areas, and I cannot see how, with the facts before L escape the conclusion that this connection must baret. either the Atlantic or the Pacific, not in high data tudes, perhaps across both.

The mastodon is not the only animal which point: lesson. The machairodus, a very highly specialized to m been found both in the Old and the New World, inhabit the great palæarctic province of Europ 1 the Rhine, nor America north of the great lakes. can jaguar, a mere variety of the Old World leopard animal with the same abnormal distribution, so are the and the Old World tapirs.

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Now this connection between the Old and the Ne cannot, so far as we can judge, have been in high inthe forms in question have not occurred in high lat the connection had been across the Northern Paat v have had some remains of these animals in Japan, than one fossil elephant has occurred; or in the Sanic which are, to all appearances, a very old land-surface

The connection inust, therefore, if it was across it ca have been across its more equatoria! part. It to follow from the absence of these animals in the h of America and Europe, save the doubtful case of k-in the case of the Atlantic also the land-bridge mas kit further south, and perhaps where the Atlantic istas main. One more inference. If there was a pea circular belt of land about the earth in the trees tropical zone over which these beasts could travel, sibly account for the tertiary climate of high lang! been a warm one, as we know it was. A zone of lat tropics would act as a furnace, whose heat would be w tributed by the ocean currents in contact with it.

The views here urged, it will be said, are like those advocates of a Miocene Atlantis. They are in var different, and meant to explain a very different phenome namely the aberrant and abnormal distribution of the and its companions. The mention of the Miocene A. however, suggests another and more critical difficulty is ing the Pliocene beds, but this must be postponed letter. HENRY H. How

The Athenæum Club, January 13.

Earthquake Shocks.

A SERIES of slight earthquake shocks have lately: this district, viz. January 3, 2.15 p.m. at Severn Junction E January 4, 11 a. m., Itton Court, Chepstow (a heavy ( in a greenhouse was seen to move four times by Mr and the Rev. N. S. Barthropp); January 5, between 201 p.m., and again on the 6th (a little earlier), Llanthony M(a rumbling noise on the Black Mountains near the m Mr. P. E. Hill); January 14, 6.55 p.m., a shock last than a second, Bigswear House, Coleford, Mr. J V. Sr (Mr. Newbery has had experience of earthquakes, bus residence in Japan). E. J. L

Shirenewton Hall, Chepstow.

The Weather of Summer.

I REGRET to find that, in making a quotation at the my letter last week (p. 246), I erred in supposing Mr to be the writer. I beg to apologize for the slip. A



subject of this communication may seem remote nd uninteresting, but it will not be difficult to at questions of the highest importance for phy, anatomy, and the Darwinian theory are closely to those touching the structure of the electric of certain fishes and the laws of their functions. fact that the body of an animal should become a te electrical apparatus acting at the will of its induces us to inquire how this extraordinary result en attained; that is, to investigate the origin of ctric organs of fishes, and the manner in which imal throws them into action. We shall see that suing both lines of enquiry we open far-reaching into regions as yet unknown.

ording to the present state of our knowledge there : no doubt that most of the electric organs hitherto ered are of muscular origin. It is not my intention ell on this transformation of muscular tissue, but it evertheless prove interesting to cite an example of

The well-known electric eel of America, Gymnotus electricus, has only the external shape of an eel, and is in reality a very short fish, carrying very powerful electric organs in a long tail springing from a very short rump. A transverse section of the tail shows that a part of the muscle is changed into electric organs, while another remains unchanged.

In the different kinds of electric skates-Torpedinidæ -the electric organs are developed from muscles, which originally belong to the branchial arches and the arch of the lower jaw.

When we look to the nerve apparatus which enables the fish to throw the electric organs into action by a voluntary impulse, we find in every case wonderfully developed ganglion cells from which the impulse is transmitted directly to the electric batteries. Such a coincidence certainly cannot be the result of mere chance. But beyond the invariable presence of large ganglion cells as the starting points of electric nerve fibres there is very little uniformity in the arrangement of these elements in the different sorts of electrical fishes; on the contrary, there are most remarkable and striking differences not only in the position but also in the number and in the


1-Transverse section of the tail of Mormyrus cyprinoides.

completeness with which such transformation can e place; I refer to the Mormyrus-the so-called pike he Nile-a fish which has only of late been sufficiently own to possess electric power. A transverse section of tail of any ordinary fish shows scarcely anything more in the vertebral column, muscles and their tendons, ached to the bones. On the other hand, a transverse tion of the tail of Mormyrus (Fig. 1) shows no conicuous muscles, but in place of them electric tissue ing up the entire space occupied by muscles in ordinary bes. Of the muscular apparatus there is nothing ft except the longitudinal tendons passing outside the ectric organs from muscles placed anteriorly. If these ndons were cut across the Mormyrus would be unable

move its tail.

Omitting the complicated arrangement of histological lements in this modified muscular tissue in the different lectrical fishes-which could not be sufficiently explained ithout a large number of illustrations-it may be suffiient to state that a kind of swelling loosens the molecular lements of the muscles and allows them to be settled gain in a very regular but quite new form.

FIG. 2.-Ganglion cells from roots of electric nerves of Torpedo.

appearance of these nerve centres. It is to be hoped therefore, that some important views regarding the character and functions of ganglion cells in general may be suggested by their study.

In the Torpedo the electric ganglion cells-being in vast numbers-form a bean-shaped mass in the medulla constituting the well-known electric lobe. It represents modified motor centres of the vagus nerve; anteriorly it is covered by the cerebellum, but emerging from beneath that organ, the lobe increases rapidly where the largest electric nerve leaves the medulla. Lower down its size again diminishes, where it gives rise to the fourth electric nerve and terminates quite free in a blunt point on each side. On counting the ganglion cells in a complete series of sections one finds the number to be about 54,000-a number that can be found to nearly correspond with the fibres in the electric nerves that arise from them. A transverse section of the medulla, close to the spot where the roots of the electric nerves are gathering, shows the so-called axis cylinder processes of the cells entering the roots to form the nerves. This is seen in Fig. 2-a photogram taken from nature like all the other illustrations of this paper.

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