which fed on the debris of both animal and vegetable nature in the undergrowth of primeval forests. Such is in fact the life of the lowest insects known to-day, some of which, such as Machilis, nourish themselves on the decaying sea-weed on the sea-shore, and retain throughout life vestigial limbs attached to the abdominal segments which aid them in their crawling movements. Now the myriapod or polypod larva survives as the caterpillar of the Lepidoptera and the primitive Hymenoptera. It is also found amongst the primitive Meuroptera and amongst the may-flies (Ephemeroptera). These last-named insects were supposed to possess a larva showing great secondary modifications, for it is provided with leaf-like gills attached to its abdominal segments; but Heymons has shown that these gills are nothing but modified abdominal legs. It is a curious fact that amongst the lower insects, such as the cockroach, this polypod stage is passed through during the embryonic phase of development. The reason for this change is that these insects lay their eggs in situations where a grub-like larva would perish, whereas the higher insects, in which the stage is larval, are gifted with instincts which lead them to lay their eggs in situations where an abundance of easily procured and easily masticated food is available and a scavenging existence like that of the ancestor is possible.

A fourth factor which modifies development, and which is potent in its effect although it is usually overlooked, is loss of size in the larva as compared with the ancestor which it represents. As conditions change and the larval life becomes more dangerous there arises a tendency in which we may trace the influence of tachygenesis to pass quickly through the larval stage and to metamorphose at as early a period of growth as possible into the adult condition. A consequence of this change is that the larva assumes a new relation to its environment, for many qualities of the surrounding medium, such as the viscosity and supporting-power of water, acquire an altered importance as the organism decreases in size. If the ancestral organs were reduced in the same scale as is the whole body of the larva, this would in many cases result in their becoming incapable of being used. As a consequence we find that in many cases where the ancestor had a series of organs, this series is represented in the larva by fewer members or only one member of larger relative size, and that where in the ancestor there was a pair of organs there is frequently only one in the larva, but this is on a larger scale than the rest of the body. If we now select a few examples to illustrate this principle, we may consider the free-swimming larva of that most primitive of all vertebrates Amphioxus. This larva has only a single series of gill-slits which are so enlarged as to occupy the whole ventral surface of the body. If the double series of slits, which the ancestor in common with all other fish possessed, had been developed in the larva, they would necessarily have been of such minute size that the capillarity of the water would have prevented them from being functional. Similarly there is no doubt that the eyes of vertebrates were from the beginning paired structures, but they are represented in the ascidian tadpole by a cup-like outgrowth of one side of the brain. Again no serious doubt can be entertained that the primitive arthropod was evolved from a long many-segmented annelid with flexible parapodia. But the most primitive larval form of the Crustacea is the nauplius which is a little, oval, unsegmented creature with but three pairs of legs. The existence of this larva was a great stumbling-block to the earlier embryologists. It seemed to indicate that the Crustacea must have been derived from an unsegmented animal totally distinct from the ancestor of other Arthropoda, for the progenitor of these must have been long and segmented since the embryos of all these Arthropoda have many segments. But if we look at the nauplius larva from the standpoint of function rather than of structure we have no difficulty in seeing in it the recapitulation of the first step in the arthropodization of the annelid. This step was a change of habits which consisted in using the foremost parapodia as oars to propel the animal and as organs to seize food. As a consequence in the front of the body the cuticle was thickened and the “arthropodous" type of limb produced, whilst in the rest of the body the annelid condition of affairs persisted as indeed it may be almost said to do in the posterior portions of the bodies of this most primitive of Crustacea, the longbodied Phyllopoda such as Artemia. Once begun in front, this "arthropodous" modification was gradually propagated backwards so as to involve the hinder segments of the body and in this way the higher Crustacea were evolved. In the nauplius larva, the anterior arthropodized portion of the ancestor with its appendages is alone represented; the hinder annelid portion in which function was less intense and less important is not developed.

One last instance of the principle may be adduced which we select from the embryology of the higher vertebrates. In the development of those types of Vertebrata in the life history of which there is a long larval phase (Cyclostomata, dipnoan, ganoid" and teleostean fish, Amphibia), a larval excretory organ termed the pronephros makes its appearance. Its duct later becomes the duct of the permanent kidney, but the pronephros itself consists of very few tubules and these originate from the wall of the general body cavity and not, as do the tubules of the permanent kidney, from special sacs

R. Heymons, "Über die Lebensweise und Entwicklung von Ephemera vulgata," Sitzungsberichte der Gesellschaft der Naturforschenden Freunde zu Berlin for 1896.

(the malpighian capsules). The earlier workers regarded the pronephros as a last trace of a primeval excretory organ of quite different structure to the permanent kidney by which it is later superseded. The works of Hatta on the development of the lamprey and of Kerr on the development of the Polypterus have proved that the pronephros is nothing more than the foremost section of the perma nent kidney, early called into action and enlarged whilst the hinder section of the metamerically repeated series of tubes of which the kidney consists remains undeveloped. These investigators have further proved that the portion of the general body cavity from which the pronephric tubules arise consists of several malpighian capsules fused together and secondarily communicating with the general body cavity.

Life History of Animals.—It might be supposed that with so many modifying factors at work it would be a hopeless task to attempt to disentangle the recapitulatory element from them, and that therefore the ancestral history of animals except in its latest and least modified chapters would remain a closed book. But when we recollect that the life history of every species constitutes a separate edition of this history, and that the modifying factors have affected no two of them to the same extent, it becomes evident that comparative embryology built on a broad basis can attack the problem with a fair prospect of success. Bearing in mind the priority of the larval over the embryonic phase, and beginning therefore our survey with the larvae of the simplest metazoa, we are able to recognize the first step in the evolution of the metazoön from the protozoa in the blastula, the hollow ball of cells which may be regarded as representing a colonial protozoön like the living Volvox. This stage was followed by the formation of a gut by the intucking of one side of the ball; and this second step is represented in the life histories of all the lower and simpler animals by the gastrula stage. Following on this stage came the formation of the coelom as a series of pouchlike outgrowths of the gut, and the change of the single opening of the gastrula, the blastopore, into two openings which became the mouth and the anus by the constriction of its middle portion. It has been possible to show that two groups so utterly diverse in appearance as the Annelida and the Mollusca have originated from a single group of free-swimming ancestors represented by the trochophore larva, and since Arthropoda are admitted by all to be descended from Annelida this conclusion involves the ancestry of four-fifths of the animal kingdom.

We can form a very plausible guess as to the nature of the diver gence of habits which led to the differentiation of the Annelida and Mollusca from one another. The original stock was free-swimming but both groups derived from it are typically bottom-dwellers. Two modes of seeking their food were open to them; they could either glide over the bottom by means of their cilia as young Gastropoda and Lamelli branchiata still do, or they could burrow into it. The first led to the evolution of Mollusca, the second to that of Annelida.

Two other groups of very diverse structure, which embryology has given strong reasons for believing to have been derived from a single race, are the Echinodermata and the Vertebrata. The lowest form which gives distinct evidence of the vertebrate affinities is the worm-like creature Balanoglossus. The larval form of Balanoglossus is a free-swimming organism called tornaria which shows the closest resemblance to the typical larva of Echinodermata, the dipleurula. The recognition of this affinity has assisted in the elucidation of a difficult subject to which considerable space was devoted in the 11th ed., viz. the origin of the central nervous system.

It is characteristic of the most primitive Annelida and Arthropoda that this system develops as a ring round the blastopore and an endeavour was made in the 11th ed. to prove that this was originally true of vertebrate embryos also. But it is a peculiarity of the vertebrate-echinoderm alliance which is still unexplained that in them the blastopore gives rise to the anus alone, whilst the mouth is formed as an apparently independent perforation at a considerably later period of development. A long succession of embryologists. with their eyes fixed only on the embryos of Annelida, Arthropoda and the higher vertebrates, have held that the vertebrate mouth is a new structure formed by the fusion of a pair of gill-slits and have prosecuted vain searches for traces of the old mouth. Others have imagined that the mid-dorsal line of the vertebrate embryo along which the nerve-cord develops corresponds to the line joining mouth and anus in the arthropod, the line in fact which is occupied by the slit-like blastopore in Peripatus. They hold that the nervous system of the vertebrate originally extended round the front ead of Hatta, "The Development of the Renal Organs in the Lamprey," Journ. Coll. Sci. Imp. Univ. Tokio, 1912. & Kerr,

Vertebrata with the exception of Mammals." Textbook of Embryology, vol. i., pp. 223-237 (1919).

the embryo so as to include the mouth. But the independent and late development of the mouth is as marked a feature in the echinoderm larva as in the vertebrate embryo and there are no gill pouches in the echinoderm on which we could fall back to explain the phenomenon. Further, in the adult echinoderm the whole of the ectoderm is underlain by a nervous plexus of which the central nervous system is only a specialized and intensified portion, and the same thing is true of the anterior region of Balanoglossus. It is therefore futile to look for exact correspondence between the central nervous systems of two stocks which diverged from one another at such a primitive level as did the Vertebrata and the Annelida. In fact the descendants of the trochophore stock (Annelida, Arthropoda and Mollusca) on the one hand and the original Vertebrata on the other seem to have adopted two different modes of life which led to concentrations of the nervous system in different parts of the body. The trochophore stock took to crawling on their ventral surfaces and their focomotor organs were developed in this region of the body and in connexion with them the motor ganglia which make up the ventral nerve-cord; whereas the vertebrate stock took to swimming by lateral blows of their blade-like bodies and this led to the concentration of the central nervous system in the mid-dorsal line.

Enough has been said to give evidence for our belief that the most recent research has tended to reëstablish the recapitulatory element as the fundamental factor in life-history, and if this be admitted the study of comparative embryology opens up a means of investigating the early history of life at a stage long before it left evidence of its existence in the stratified rocks; and, further, the acceptance of recapitulation involves a conception of the laws of heredity entirely distinct from and supplementary to that suggested by Gregor Mendel and his followers.

BIBLIOGRAPHY.-F. R. Bailey and A. M. Miller, Textbook of Embryology (1909); F. M. Balfour, A Treatise of Comparative Embryology, vols. i. and ii. (1881); A. Brachet, “L'Euf et les Facteurs de l'Ontogenèse," Encyclopédie Scientifique, Paris (1916); J. C. Heisler, Textbook of Embryology for Medical Students (1907); H. Driesch, The Science and Philosophy of the Organism; Gifford lectures for 1907 and 1908; O. Hertwig, Lehrbuch der Entwicklungsgeschichte des Menschen und der Wirbelthiere, Jena, 1890-1920; J. W. Jenkinson, Vertebrate Embryology (2nd ed. 1921), Experimental Embryology (1909), Three Lectures on Experimental Embryology (1917); J. Graham Kerr, Textbook of Embryology, vol. ii., Vertebrata (exc. Mammalia) (1919); Korschalt and Heider, Textbook of the Embryology of the Invertebrates, translated by E. Mark, Ph.D., and W. McM. Woodworth (1895); Lillie, The Development of the Chick; E. W. MacBride, Textbook of Embryology, vol. i., Invertebrata (1914); A. Milnes Marshall, Vertebrate Embryology (1893); T. H. Morgan, Regeneration (1901). (E. W. MACB.)

ENCEPHALITIS LETHARGICA (from Gk. ¿yкéaλov, a portion of the brain, and An@apyos, forgetful), a specific infectious disease of the nervous system, of which the most frequent, though by no means invariable, symptom is drowsiness or lethargy, often associated with paralysis of the muscles of the eye, producing diplopia or double vision.

In recent years this disease first appeared in epidemic form in Austria in the winter of 1916, and was described and named by C. von Economo in Vienna in 1917. It reappeared in the following winter, and was recorded in France in March 1918 by A. Netter. In England it was first recorded in April 1918, independently by Wilfred Harris and A. J. Hall. These earlier epidemics were all recognized by the combination of lethargy and diplopia. Subsequently the same seasonal incidence has prevailed, the number of cases diminishing in summer and increasing in winter and spring. In the United States it was reported in March 1919, the epidemic having spread from east to west.

The literature of medicine has been ransacked to ascertain whether or not previous records exist of the occurrence of the characteristic combination of symptoms. In 1890 a small epidemic occurred in North Italy, and later in Austria and other countries, which may be accepted as Encephalitis Lethargica. At the time it was known as Noma. It attracted little attention. The evidence for sporadic cases since then is doubtful.

Previous records are all doubtful. Hippocrates, Sydenham and other less-known authorities have described conditions which

may or may not have been Encephalitis Lethargica. Stahl in 1779 recorded more fully an outbreak characterized both by lethargy and diplopia, and with other very suggestive symptoms. Franck in 1837 divided Encephalitis into various types, including a lethargic form which he stated occurred frequently as a result

Whether or not the observed combinations of symptoms have ever occurred before, the question early arose whether the syndrome should be regarded as a clinical entity or as a special manifestation of some disease previously known in other forms. The three diseases with which its relations have been more particularly considered are botulism, influenza and acute poliomyelitis or Heine-Medin's disease. Botulism results from the consumption of infected meat or other food, usually ham, and is especially characterized by paralysis of the eye muscles. The disease is due to infection with a specific bacterium-the bacillus botulinus. Since the most careful search has invariably failed to detect the presence of this bacillus in Encephalitis Lethargica botulism can be finally excluded. With regard to influenza, the appearance of Encephalitis Lethargica, including Noma as such, has approximately coincided with epidemics of influenza in 1889 and at the present time. On the other hand, there is considerable evidence against their identity. Influenza is highly contagious, while the clinical appearance of Encephalitis Lethargica occurs in an irregular manner and has not attained any great magnitude as an epidemic. When Encephalitis Lethargica commenced in Austria influenza had not yet appeared. There are also histological differences, since in influenzal encephalitis there is marked oedema of the brain and an absence of the two special characteristics of Encephalitis Lethargica—vascular congestion and infiltration of the perivascular lymph spaces. Pfeiffer's bacillus, the so-called influenza bacillus, is not found in Encephalitis Lethargica.

The relations of Encephalitis Lethargica to Heine-Medin's disease have led to much discussion. Unusual forms unquestionably occur in which the diagnosis is doubtful, both on clinical and pathological grounds, but, considering typical forms, there are striking differences between the two diseases. Heine-Medin's disease particularly attacks persons under 20 years of age, and tends to increase in frequency in summer. The onset of the general symptoms and of the paralysis is acute, the course is brief and the spinal cord is mainly affected. In Encephalitis Lethargica, on the other hand, persons of all ages are liable to attack, and the frequency is greatest in winter and spring. The onset is usually insidious, the course is lengthy, and the mid-brain is especially affected. Histologically there are also important differences. Microscopic haemorrhages are constant in Heine-Medin's disease, while perivascular infiltration is slight, the reverse being true of Encephalitis Lethargica.

Symptoms. Encephalitis Lethargica was primarily recognized by the occurrence of the combination of lethargy and double vision, the latter being due to paralysis of the muscle of the eye. While pathological drowsiness in varying degrees is probably present in 70 to 80 per cent of cases at some stage of their course, further observation has revealed the occurrence of numerous other manifestations. The disease is widespread through the nervous system, and the complexity of the structure of the nervous tissues, together with the high degree of specialization of the functions of its various

parts, explains the protean nature of its symptoms. Numerous

types" have been described, but the value of these is slight, as a single patient in the course of a few days often exhibits the characteristics of many such types. The clinical manifestations are probably best classified as Walshe suggested, according to the broad scheme proposed for other nervous diseases many years ago by Hughlings Jackson. In the following description based on this system, positive" symptoms denote exaltation of function, which may be due either to irritation of nervous tissue or to a loss of the control exercised normally by the higher centres of the brain, while "negative" symptoms denote depression or loss of function principally due to destruction of nervous tissue.

A. General Symptoms Due to Toxic Infection.-These include weakness, headache, often occipital with some stiffness of the neck, shivering, vertigo, muscular pains and vomiting or other gastro-intestinal disturbances. The pulse may be rapid and eruptions, usually resembling measles, occasionally occur. The temperature is variable, and it has no characteristic course. It often rises after some days from 101° to 105° F. for a short period, but may be more B.

prolonged, or pyrexia may be absent throughout.

Nervous Symptoms.-These are general and focal, the latter being due to affection of highly specialized portions of the brain. (1) General Nervous Symptoms.—Positive symptoms are delirium, mania, restlessness and various degrees of excitement, while the more common negative manifestation is the characteristic lethargy, in all grades from simple apathy to complete coma. Innumerable

companies), were needed to carry out work behind the field companies in the front line, electrical and mechanical companies to deal with machinery of all sorts, army workshops companies, base park and advanced park companies to feed the insatiable demands of the fighting line for prepared trench materials and other such requirements. For mining warfare, tunnelling companies, officered by mining engineers, were enlisted and did magnificent service. For water supply, boring sections were needed, and in Egypt water-supply companies; for surveying, field survey battalions and companies, and for sound-ranging and observation (in conjunction with artillery) special sections and groups were formed. The inundation of some parts of the line and the land drainage of others demanded special sections, mostly enlisted in the English Fens. Field and anti-aircraft searchlights absorbed a large number of sections. Timber supply became a matter of urgent importance in the second year of the war, and forestry companies had to be formed to fell and prepare the quantities of timber needed for field engineering. The science of camouflage called for special units to deal with the provision and erection of concealing material. Chemical warfare demanded specialists both in preparing and projecting the new element of war. Meteorology played a new and important part, and it too required special units to take and record observations. The army post-office work devolved on the Royal Engineers. All these were altogether apart from the signal units, already touched upon. There was, further, the transportation branch, which ⚫ formed a large and important feature in the area behind the line, and was divided into two main organizations (subsequently combined under one director-general), viz. Roads and Railways, and Inland Water Transport.

The former had railway construction companies, survey and reconnaissance section, a railway signal and interlocking company, wagon erecting companies, broad gauge workshop companies, and miscellaneous trades companies, with electrical sections; light railways operating companies, train crew companies, and forward companies, also miscellaneous trades companies, workshop companies, and light tractor repair companies. There were also training schools, chiefly for light railway work. There were numerous traffic sections, and broad gauge operating companies; there was a transportation stores company, and a steam boiler repair company. In connexion with roads there were several road construction companies, and quarry companies with a quarry maintenance section, most of these enlisted in the Welsh quarries.

The Inland Water Transport had headquarters' units at various places in England-Richborough, where a magnificent new port was built, Southampton and Poplar. There were workshops and shipyard companies, and construction companies at Richborough and several other places in England, and port construction companies at many ports in France. There were marine companies, traffic companies and train ferry companies in England, while in France there were sections working all over the canals on the army areas, with headquarters at Aire.

In Egypt there were sections at Alexandria, on the Suez Canal, and at various places on the Nile; in Italy at Taranto; in E. Africa at Dar-es-Salam and some other ports; in Russia at Murmansk. But perhaps the greatest work done by this branch, except in France, was in Mesopotamia, where the organization at Basra included vessels, marine engineering, accounts, dockyards and shipbuilding, native craft, I.W.T. Stores, buoyage and pilotage, conservancy and reclamation, camps, coal depot, barge depot and construction H.Q., both on the Tigris and Euphrates. There were detachments at various places on each of the great rivers, and on the Persian lines of communication at Karun and Ahwaz, and also at Muscat.

At the outbreak of war the corps of R.E. consisted of 1,831 officers and 24,172 other ranks. On Nov. 11 1918 there were 17,711 officers and 322,739 other ranks. The above figures include regulars, special reserve, territorials, and all signal and transportation units, but not from overseas or India.

As regards troops from overseas it is perhaps sufficient to say that their strength was in proportion normally to the total numbers of all arms, but that in addition there were tunnelling companies from the Australian and Canadian mines (who did good service in France and in Palestine), and forestry battalions from the backwoods of Canada, who did most useful work in France, and also in Cyprus for the supply of timber to the armies operating in the eastern Mediterranean littoral.

Mention may here be interposed of two cognate organizations, one of which never was actually incorporated in the R.E.; the other

was part of the R.E. at one time, but was allowed gradually to disappear, or be merged in corps raised for work other than R.E. The former were the pioneer infantry battalions, to be supplementary to R.E. labour, on the principle well known in India, where such battalions, officered by infantry officers, and trained to a greater extent in field engineering than the average line battalions, had proved most useful. There was one such battalion per division, and the intention was that they should normally be associated, much more closely than other infantry, with the field companies Royal Engineers. The labour battalions, II of which were raised, were all of the professional navvy class, all over military age, and officered by civil engineers, architects, surveyors, etc. They did excellent work and of a nature which was by no means unskilled. Whether the later policy of absorbing the personnel into labour companies, who did absolutely unskilled work (unloading ships, etc.), was wise, cannot be here discussed, but it had the effect of removing from the engineers' control a very valuable body of men.

One other Indian innovation was also introduced, viz., the appointment to corps and armies of field engineers and assistant field engineers, i.e. officers of civil-engineering experience (either R.E. or civilian) whose business it was to execute works, in the area of their corps or armies, by means of civil labour.

Organization at Headquarters and in the Field.-At the War Office the organization for developing and controlling not only the personnel, briefly indicated above, but also the design and execution of works and the design and provision for engineering equipment and plant, was divided among three of the principal branches of the Department, viz., one section under the adjutantgeneral had to raise and maintain all the above units; under the quartermaster-general the director of movements had to organize and control the transportation branches (railways and I.W.T.), while the director of fortifications and works and the branch of the master-general of the ordnance were responsible for all the technical design and execution of engineering works at home, and for supplying the varied and complicated machinery and plant for the engineering needs of the armies in the various theatres of war. This involved also the carrying-out of a series of experiments on all sorts of inventions, though after the war had progressed for some time this duty was partly taken over by the Ministry of Munitions, which in other respects did not. supply military engineering needs.

The works directorate was divided into 12 branches, each under a senior officer of engineers:-(1) Rifle ranges, artillery practice grounds and lands generally; (2) hutted camps and barracks; (3) coast fortifications (on the E. coast of Great Britain especially); (4) ordnance store buildings; (5) aviation buildings, until Jan. 1918, when the Air Ministry was formed; (6) design branch, for evolving and coordinating all designs; (7) personal matters arising out of the employment of civilian engineers, electricians, foremen, surveyors, etc., on military works, in themselves a large host; (8) mechanical engineering and supply of stores connected therewith to armies; (9) electrical stores and experiments, which included the inspection branch, also telephone factories, and a wireless experimental station; (10) liaison branch with all armies in field, dealing with all miscellaneous needs; (11) experimental and equipment section; (12) contracts, schedules of prices, and quantity surveying. Temporary training schools and depots were found, not only at Chatham and Aldershot for dismounted and mounted men as usual, but at Longmoor for railway men, at Hitchin and Bedford for signallers, at Newark, Deganwy (N. Wales), Irvine (Ayrshire), Buxton, and Brightlingsea (Essex) for training sappers. The wireless experimental section at Woolwich and the electric light school at Portsmouth also were valuable training depots.

As regards the organization in the field there was at first neither an engineer-in-chief nor a chief engineer for each army. There were senior engineer officers, one at G.H.Q. and one at the H.Q. of each corps, but their duties were advisory only, and they had no power of purchase, or of engaging civil labour. This organization was a deplorable legacy from the S. African War, when the nature of the campaign was so different from that in Europe.

On the lines of communication, on the other hand, there was a director of works, with a proper staff and adequate powers, but he had no part in any military operations, nor, judging from the Field Service Regulations, was it contemplated that, except in the rare possibility of a siege, there would be anything in the nature of engineering in war that could not easily be done by the field companies under their divisional generals. These numbered two per division under a lieutenant-colonel. In 1911 a committee under Lord Kitchener had recommended raising the number to three. But in 1914 this had not been carried into effect, many officers of experience considering that such increase, though possibly desirable, was not a matter of urgency. The first few weeks of the war altered all this. A new organization became imperatively necessary, and the increase of personnel was nowhere more marked than at G.H.Q.;

whereas in 1914 the entire staff of engineer officers at G.H.Q. was one brigadier-general, in 1918 this staff was one major-general, two brigadiers and 19 other officers. Similarly the engineer staff of each army was increased from one to 11 officers-one for water supply, another for bridging, others for mining, camouflage, stores and so on. The field companies, whose losses in the first few weeks of the war were very great, were increased at once from two to three per division, and a pioneer battalion in addition gave each divisionalgeneral a sufficient supply of both skilled and unskilled labour for him to make tactical use of engineering works. It was not intended that these troops should be used as infantry except in the gravest emergency, although in some cases this was not borne in mind, and the casualties which resulted made the want of such technical troops more acutely felt than ever.

Under the direct orders of the chief engineer of an army corps there were two or three army troops companies R.E., two or three tunnelling companies, a company or two of a labour battalion, and miscellaneous working parties and transport lorries.

Field Companies.-As the field companies were the most numerous of all the RE units (there were some 160 of them in France in 1918) as well as being the normal organization of military engineerscorresponding to a battalion of infantry, a squadron of cavalry and a field battery of artillery-it may be as well here to say a little about their organization. The field companies of the regular army (of which there were 13 in 1914) were formed about 1879 by adding to a few selected fortress companies a section of mounted drivers with transport to carry ordinary entrenching tools, and the special tools needed for the various tradesmen of which the company was composed. At that time the companies were almost exclusively emploved on barrack maintenance, and, while subject to military discipline and trained as infantry in drill and musketry, they were given little or no special training as field engineers. But from the experience of the Egyptian and Sudanese campaigns of 1882-5 there began a steady improvement in their rôle as a valuable tactical arm. About 1885 each company was taken off the works annually for a course of field work instruction. In 1889 continuous engineer's pay, instead of working pay for actual hours spent on works, was introduced, a matter of the utmost importance, for it enabled men to be taken for military training without penalizing them in respect of pay, while their trade skill could still be economically utilized on works when they were not otherwise employed. The gradual improvement in the military training of this arm, and its cooperation with other arms, was, after the S. African War, still further developed by having the companies posted to army divisions under the direct responsibility of division headquarters, and by the participation, by all ranks, in the divisional training schemes. Further, young civil engineers were, by arrangement with the Institution of Civil Engineers, given commissions in the R.E. Special Reserve, and after some preliminary training were attached to field companies.

Each company consisted of six officers, all mounted, with about 220 other ranks, of whom about 75% (dismounted) were tradesmen, the remainder being drivers. There were some 60 horses and mules, with the following vehicles:-four double tool carts for tools and equipment, three pontoon and trestle wagons for bridging plant, and a special vehicle for explosives, sandbags, cordage, etc., with the general transport vehicles appropriate to a unit of this size and composition. The company was organized in four sections, each under a subaltern, so that each section could be detached, with its own tools, for some specific task. There were also some pack animals to take tools, etc., to places where wheeled vehicles could not go. A certain number of the dismounted men were cyclists whose business it was to reconnoitre ahead and bring in information.

Although the greater part of the sappers (dismounted men) were skilled tradesmen, there was introduced, shortly before the outbreak of war, a certain dilution of skilled labour in the form of "pioneers," men who were trained in ordinary field work, but had not been taught a trade before entering the army. Whether this dilution was on the whole satisfactory is a matter on which there is difference of opinion. There is, however, no doubt that as regards the officers, the greater their knowledge and experience of engineering work the better, owing to the variety of the work that falls on a field company in war. Moreover, the development of weapons and the weight of guns, tanks, etc., which came to be used in the war revolutionized much of the previous practice. No longer were combinations of timber, brushwood and earth sufficient for field defences, nor pontoons and spar bridges sufficient to cross rivers. Concrete and steel had come into the field, and the engineers accustomed to use these in peace had to take them in hand for war, and to see that rapidity of construction was combined with stability and strength.

Broadly speaking, the duties of the field companies were field defences, mining, demolitions, water supply and distribution, and temporary roads and bridges, in the fighting zone. Behind these came the army troops companies R.E. and the many special units whose duties are indicated by their nomenclature.

The School of Military Engineering. It is evident that to train officers and men-the former especially-for the varied tasks that lie before them in war, some very special instruction is needed in peace. This is supplied by the School of Military Engineering at Chatham, to which every R.E. officer after receiving his first commission is sent for a course of instruction, lasting normally two years.

This school owes its origin to the Peninsular War. In that campaign at first there were no trained sappers, and the officers of the R.E. were woefully ignorant of such military subjects as the demolition of bridges. As a result of Lord Wellington's representations, and the advocacy of an able engineer-officer, Col. Pasley, a school of instruction in siege works was begun in 1812 at Brompton barracks, Chatham. In course of time instruction in other branches, eg. construction, surveying, electrical and mechanical engineering, chemistry, astronomy, etc., was added; and in spite of certain disadvantages, e.g. the growth of houses and establishments round the school, and the absence of troops of other arms with whom combined training could be carried out, the work done at this school has been of the utmost value both in war and in peace, for officers and men trained there have gone to all parts of the Empire and made their mark in works of public utility and permanent value. The training in the pre-war period was as follows:-The two years' course is approximately divided into four equal parts under each of the chief instructors, in field fortification, construction, surveying and electricity. The officers are attached to depot companies in ore or other of the battalions of R.E. under training, and thus, concurrently with their technical training, they learn the routine of military administration, discipline and drill. As regards the four main courses of instruction it is evident that in the short time available only the rudiments of each subject can be taught. In a profession which admits of so many different avenues of service to the country it is evident that the preliminary course of instruction should include that which is likely to be of value in each and every capacity. There must be a difficulty in arranging such a course when it is borne in mind that one officer may devote his life to purely military studies, another to the scientific work of, say, the Survey of India, another to railway constructions, another to electric de velopments and so on. Yet there is doubtless some common ground in which all must be trained before diverging, and this is the object of the Chatham training. In field fortification, besides the prin-` ciples of defence, already learned by the officers in the cadet stage of their career, there is the practice of entrenchments, redoubts, military mining and demolition; there is, further, construction of light railways and of field shelters, water-supply expedients, and other miscellaneous subjects. This course is largely out of doors, and is specially valuable in teaching young men how to organize and handle skilled and unskilled labour. The survey course includes instruction in all surveying instruments and in the practice both of large survey operations and of the rapid operations frequently necessary in military exploration, and in combining the work of several observers in an unknown country. In the construction course lectures are given on building materials and builders' trades, on applied me. chanics and hydraulics, on water supply, sanitary engineering, roads and railways, the design of structures, including bridges, reservoir walls, etc., and the ordinary methods of execution. Visits to engineering works in progress are included in the course.

Theory and practice are combined in this as well as in the mechanical and electrical engineering courses, the details of which are on similar lines. Care is taken to keep in close touch with the best civil-engineering practice in the country; eminent civil en gineers are invited every winter to deliver lectures, and after the completion of the course selected officers are sent to work for six or eight months on one of the great railway lines, either to learn trame control, or to be more thoroughly equipped in mechanical engi neering in the railway workshops. Other officers go to the electric light school at Portsmouth for special training. (G. K. S.-M.)

United States.-The army which in its circumstances bears the closest resemblance to the English is that of the United States. Both countries recruit their armies by voluntary enlistment, and both use to some extent their military engineers, after completion of their training at a military school, in some form of civil-engineering service in peace.

From 1901 to 1916, the maximum authorized strength of the Corps of Engineers was 248 officers of all ranks, and 1,008 enlisted men forming 3 battalions of 4 companies each. The officers not needed for service with the troop units were employed on civil public works, inasmuch as the Corps of Engineers is charged with the improvement of harbours and rivers, both coastal and inland. As in the case of English officers in the civilengineering departments in India and the colonies, this employment proved to be of great value in war in that it had trained them "to take heavy responsibilities; in the habit of making weighty decisions; meeting sudden emergencies; in the organization, operation and care of large bodies of men; and working with men not familiar with or subject to [army] discipline."

In the United States, officers for the Corps of Engineers are obtained from two principal sources, namely, the U.S. Military Academy at West Point, and the leading civilian engineering colleges. The Military Academy is not an engineering school, and, although the course furnishes a good foundation for an