Chapter 4

Fig. 12.This figure should be examined with a magnifying glass. It is a direct reproduction of a photograph of a detached nebula and surrounding stars in Cygnus by Dr. Max Wolf of Heidelberg (reproduced by permission from the Monthly Notices of the Royal Astronomical Society, vol. lxiv, Plate 18, p. 839, q.v.). The exposure was four hours on July 10th, 1904, with a camera the lenses of which have a diameter of sixteen inches. The picture is enlarged so that the apparent diameter of the Sun or Moon would be about 1⅓ inch on the same scale (one minute, or sixtieth of a degree, equals one millimetre).The “apparent diameter” of the sun or moon is about one in 115: that is to say that a covering disc of any size you like can be made exactly to coincide with and “cover” the disc of the sun or moon provided that you place it at a distance from the eye equal to 115 times its own diameter—thus a disc of an inch in diameter (say a halfpenny) will just “cover” the sun or moon if placed at a distance from the eye of a little less than ten feet, a threepenny piece will cover it at about six feet, and a disc of somewhat less than half that size when held at arm’s length.The nebula (on the horizontal A A) is seen surrounded by a dark space—at the end of a long dark lane or “rift” which reminds us of the track left by a snowball rolled along in the snow. Has the nebula in some mysterious way swept up the stars in its journey through space? We cannot at present either affirm or deny such interpretations.One or two of the brightest of the surrounding starsmightjust be seen by an acute eye unaided by a telescope—but no more. The best existing telescopes would showonlythe large nebular body onthe line A A,and the larger white spots; the finest dust-like particles are stars of which the existence is only demonstrated by prolonged photographic exposures such as this, with a lens which focuses its image on to thedryplate. The old “wet-plate” would not remain wet sufficiently long to “take” the picture.It should be borne in mind in looking at this picture that each of the minutest white spots is probably of at least the same size as our own sun: further, that each is probably surrounded by a planetary system similar to our own.

This figure should be examined with a magnifying glass. It is a direct reproduction of a photograph of a detached nebula and surrounding stars in Cygnus by Dr. Max Wolf of Heidelberg (reproduced by permission from the Monthly Notices of the Royal Astronomical Society, vol. lxiv, Plate 18, p. 839, q.v.). The exposure was four hours on July 10th, 1904, with a camera the lenses of which have a diameter of sixteen inches. The picture is enlarged so that the apparent diameter of the Sun or Moon would be about 1⅓ inch on the same scale (one minute, or sixtieth of a degree, equals one millimetre).The “apparent diameter” of the sun or moon is about one in 115: that is to say that a covering disc of any size you like can be made exactly to coincide with and “cover” the disc of the sun or moon provided that you place it at a distance from the eye equal to 115 times its own diameter—thus a disc of an inch in diameter (say a halfpenny) will just “cover” the sun or moon if placed at a distance from the eye of a little less than ten feet, a threepenny piece will cover it at about six feet, and a disc of somewhat less than half that size when held at arm’s length.The nebula (on the horizontal A A) is seen surrounded by a dark space—at the end of a long dark lane or “rift” which reminds us of the track left by a snowball rolled along in the snow. Has the nebula in some mysterious way swept up the stars in its journey through space? We cannot at present either affirm or deny such interpretations.One or two of the brightest of the surrounding starsmightjust be seen by an acute eye unaided by a telescope—but no more. The best existing telescopes would showonlythe large nebular body onthe line A A,and the larger white spots; the finest dust-like particles are stars of which the existence is only demonstrated by prolonged photographic exposures such as this, with a lens which focuses its image on to thedryplate. The old “wet-plate” would not remain wet sufficiently long to “take” the picture.It should be borne in mind in looking at this picture that each of the minutest white spots is probably of at least the same size as our own sun: further, that each is probably surrounded by a planetary system similar to our own.

The “apparent diameter” of the sun or moon is about one in 115: that is to say that a covering disc of any size you like can be made exactly to coincide with and “cover” the disc of the sun or moon provided that you place it at a distance from the eye equal to 115 times its own diameter—thus a disc of an inch in diameter (say a halfpenny) will just “cover” the sun or moon if placed at a distance from the eye of a little less than ten feet, a threepenny piece will cover it at about six feet, and a disc of somewhat less than half that size when held at arm’s length.

The nebula (on the horizontal A A) is seen surrounded by a dark space—at the end of a long dark lane or “rift” which reminds us of the track left by a snowball rolled along in the snow. Has the nebula in some mysterious way swept up the stars in its journey through space? We cannot at present either affirm or deny such interpretations.

One or two of the brightest of the surrounding starsmightjust be seen by an acute eye unaided by a telescope—but no more. The best existing telescopes would showonlythe large nebular body onthe line A A,and the larger white spots; the finest dust-like particles are stars of which the existence is only demonstrated by prolonged photographic exposures such as this, with a lens which focuses its image on to thedryplate. The old “wet-plate” would not remain wet sufficiently long to “take” the picture.

It should be borne in mind in looking at this picture that each of the minutest white spots is probably of at least the same size as our own sun: further, that each is probably surrounded by a planetary system similar to our own.

Astronomy.—A biologist may well refuse to offer any remarks on his own authority in regard to this earliest and grandest of all the sciences. I will therefore at once say that my friend the Savilian Professor of Astronomy in Oxford has turned my thoughts in the right direction in regard to this subject. There is no doubt that there has been an immense ‘revival’ in astronomy since 1881; it has developed in every direction. The invention of the ‘dry plate,’ which has made it possible to apply photography freely in all astronomical work, is the chief cause of its great expansion. Photography was applied to astronomical work before 1881, but only with difficulty and haltingly. It was the dry-plate (seeFig. 12) which made long exposures possible, and thus enabled astronomers to obtain regular records of faintly luminous objects such as nebulæ and star-spectra. Roughly speaking, the number of stars visible to the naked eye may be stated as eight thousand: this is raised by the use of our best telescopes to some hundred million. But the number which can be photographed is indefinite and depends on length of exposure: some thousands of millions can certainly be so recorded.

The serious practical proposal to ‘chart the sky’ by means of photography certainly dates from this side of 1881. The Paris Conference of 1887, which made an international scheme for sharing the sky among eighteen observatories (still busy with the work, and producing excellent results), originated with photographs of the comet of 1882, taken at the Cape Observatory.

Professor Pickering, of Harvard, did not join this co-operative scheme, but has gradually devised methods of charting the sky very rapidly, so that he has at Harvard records of the whole sky many times over, and when new objects are discovered he can trace theirhistorybackwardsfor more than a dozen years by reference to his plates. This is a wonderful new method, a mode of keeping record of present movements and changes which promises much for the future of astronomy. By the photographic method hundreds of new variable stars and other interesting objects have been discovered. New planets have been detected by the hundred. Up to 1881 two hundred and twenty were known. In 1881 only one was found; namely, Stephania, being No. 220, discovered on May 19. Now a score at least are discovered every year. Over 500 are now known. One of these—Eros—(No. 433) is particularly interesting, since it is nearer to the sun than is Mars, and gives a splendid opportunity for fixing with increased accuracy the sun’s distance from the earth. Two new satellites to Saturn and two to Jupiter have been discovered by photography (besides one to Jupiter in 1892 by the visual telescope of the Lick Observatory). One of the new satellites of Saturn goes round that planet thewrong way, thus calling for a fundamental revision of our ideas of the origin of the solar system.

The introduction of photography has made an immense difference in spectroscopic work. The spectra of the stars have been readily mapped out and classified, and now the motions in the line of sight of faint stars can be determined. This ‘motion in the line of sight,’ which was discernible but scarcely measurable with accuracy before, now provides one of the most refined methods in astronomy for ascertaining the dimensions and motions of the universe. It gives us velocities in miles per second instead of in an angular unit to be interpreted by a very imperfect knowledge of the star’s distance. The method, initiated practically by Huggins thirteen years before, was in 1881 regarded by manyastronomers as a curiosity. Visual observations were begun at Greenwich in 1875, but were found to be affected by instrumental errors. The introduction of dry plates, and their application by Vogel in 1887, was the beginning of general use of the method, and line-of-sight work is now a vast department of astronomical industry. Among other by-products of the method are the ‘spectroscopic doubles,’ stars which we know to be double, and of which we can determine the period of revolution, though we cannot separate them visually by the greatest telescope.

Work on the sun has been entirely revolutionised by the use of photography. The last decade has seen the invention of the spectro-heliograph—which simply means that astronomers can now studyin detailportions of the sun of which they could previously only get a bare indication.

More of the same story could be related, but enough has been said to show how full of life and progress is this most ancient and imposing of all sciences.

A minor though very important influence in the progress of astronomy has been the provision, by the expenditure of great wealth in America, of great telescopes and equipments.

In 1877 Sir George Darwin started a line of mathematical research which has been very fruitful and is of great future promise for astronomy. As recently as last April, at the Royal Astronomical Society, two important papers were read—one by Mr. Cowell and the other by Mr. Stratton—which have their roots in Sir George Darwin’s work. The former was led to suggest that the day is lengthening ten times as rapidly as had been supposed, and the latter showed that in all probability the planets had all turned upside down since their birth.

And yet M.Brunetière and hisfriends wish us to believe that science is bankrupt and has no new things in store for humanity.

Geology.—In the field of geological research the main feature in the past twenty-five years has been the increasing acceptance of the evolutionary as contrasted with the uniformitarian view of geological phenomena. The great work of Suess, ‘Das Antlitz der Erde,’ is undoubtedly the most important contribution to physical geology within the period. The first volume appeared in 1885, and the impetus which it has given to the science may be judged of by the epithet applied to the views for which Suess is responsible—‘the New Geology.’ Suess attempts to trace the orderly sequence of the principal changes in the earth’s crust since it first began to form. He strongly opposes the old theory of elevation, and accounts for the movements as due to differential collapse of the crust, accompanied by folding due to tangential stress. Among special results gained by geologists in the period we survey may be cited new views as to the origin of the crystalline schists, favouring a return to something like the hypogene origin advocated by Lyell; the facts as to deep-sea deposits, now in course of formation, embodied in the ‘Challenger’ reports on that subject: the increasing discrimination and tracking of those minor divisions of strata called ‘zones’; the assignment of the Olenellus fauna of Cambrian age to a position earlier than that of the Paradoxides fauna; the discovery of Radiolaria in palæozoic rocks by special methods of examination, and the recognition of Graptolites as indices of geological horizons in lower palæozoic beds. Glacially eroded rocks in boulder-clays of permo-carboniferous age have been recognised in many parts of the world (e.g., Australia and South Africa), and thusthe view put forward by W. T. Blanford as to the occurrence of the same phenomena in conglomerates of this age in India is confirmed. Eozoon is finally abandoned as owing its structure to an organism. The oldest fossiliferous beds known to us are still far from the beginning of life. They contain a highly developed and varied animal fauna—and something like the whole of the older moiety of rocks of aqueous origin have failed as yet to present us with any remains of the animals or plants which must have inhabited the seas which deposited them. The boring of a coral reef initiated by Professor Sollas at the Nottingham meeting of the British Association in 1893 was successfully carried out, and a depth of 1,114½ feet reached. Information of great value to geologists was thus obtained.

Fig. 13.The Freshwater Jelly-fish of Regent’s Park (Limnocodium Sowerbii) magnified five times linear.It was discovered in the tropical lily tank of the Botanical Gardens in June, 1880, and swarmed in great numbers year after year—then suddenly disappeared. It has since been found in similar tanks in Sheffield, Lyons, and Munich. Only male specimens were discovered, and the native home of the wonderful visitor is still unknown.

The Freshwater Jelly-fish of Regent’s Park (Limnocodium Sowerbii) magnified five times linear.It was discovered in the tropical lily tank of the Botanical Gardens in June, 1880, and swarmed in great numbers year after year—then suddenly disappeared. It has since been found in similar tanks in Sheffield, Lyons, and Munich. Only male specimens were discovered, and the native home of the wonderful visitor is still unknown.

The Freshwater Jelly-fish of Regent’s Park (Limnocodium Sowerbii) magnified five times linear.

It was discovered in the tropical lily tank of the Botanical Gardens in June, 1880, and swarmed in great numbers year after year—then suddenly disappeared. It has since been found in similar tanks in Sheffield, Lyons, and Munich. Only male specimens were discovered, and the native home of the wonderful visitor is still unknown.

Fig. 14.The minute polyp attached to the rootlets of water-plants—from which the Jelly-fishLimnocodiumwas found to be ‘budded off.’

Fig. 14.

The minute polyp attached to the rootlets of water-plants—from which the Jelly-fishLimnocodiumwas found to be ‘budded off.’

Fig. 15.One of the peculiar sense-organs from the edge of the swimming disc ofLimnocodium. C, cavity of capsule; EC, ectoderm; EN, endoderm. Sense-organs of identical structure are found in the Freshwater Jelly-fish of Lake Tanganyika and in no other jelly-fish.

Fig. 15.

One of the peculiar sense-organs from the edge of the swimming disc ofLimnocodium. C, cavity of capsule; EC, ectoderm; EN, endoderm. Sense-organs of identical structure are found in the Freshwater Jelly-fish of Lake Tanganyika and in no other jelly-fish.

Animal and Vegetable Morphography.—Were I to attempt to give an account of the new kinds of animals and plants discovered since 1881, I should have to offer a bare catalogue, for space would not allow me to explain the interest attaching to each. Explorers have been busy in all parts of the world—in Central Africa, in the Antarctic, in remote parts of China, in Patagonia and Australia, and on the floor of the ocean as well as in caverns, on mountain tops, and in great lakes and rivers. We have learnt much that is new as to distribution; countless new forms have been discovered, and careful anatomical and microscopical study conducted on specimens sent home to our laboratories. I cannot refrain from calling to mind the discovery of the eggs of the Australian duck-mole and hedgehog; the freshwater jelly-fish (figs. 13,14, and15) of Regent’s Park, the African lakes (fig. 16) and the Delaware River; the marsupial mole of Central Australia; the okapi (figs. 17,18, and19); the breeding and transformations of thecommon eel (fig. 20); the young and adult of the mud-fishes of Australia, Africa, and South America; the fishes of the Nile and Congo; the gill-bearing earth-worms and mud-worms; the various forms of the caterpillar-likePeripatus; strange deep-sea fishes, polyps and sponges.

Fig. 16.The Freshwater Jelly-fish of Lake Tanganyika (Limnocnida Tanganyicae), magnified five times linear. Since its discovery in Tanganyika it has been found also in the Lake Victoria Nyanza and in pools in the Upper Niger basin.

The Freshwater Jelly-fish of Lake Tanganyika (Limnocnida Tanganyicae), magnified five times linear. Since its discovery in Tanganyika it has been found also in the Lake Victoria Nyanza and in pools in the Upper Niger basin.

Fig. 17.The Giraffe-like animal called the Okapi, discovered by Sir Harry Johnston in the Congo Forest. Photograph of the skin of a female sent home by him in 1901, and now mounted and exhibited in the Natural History Museum.

The Giraffe-like animal called the Okapi, discovered by Sir Harry Johnston in the Congo Forest. Photograph of the skin of a female sent home by him in 1901, and now mounted and exhibited in the Natural History Museum.

Fig. 18.Two “bandoliers” cut by the natives from the striped part of the skin (the haunches) and at first supposed to be bits of the hide of a new kind of Zebra. These were sent home by Sir Harry Johnston in 1900.

Two “bandoliers” cut by the natives from the striped part of the skin (the haunches) and at first supposed to be bits of the hide of a new kind of Zebra. These were sent home by Sir Harry Johnston in 1900.

The main result of a good deal of such investigation is measured by our increased knowledge of the pedigree of organisms, what used to be called ‘classification.’ The anatomical study by the Australian professors, Hill and Wilson, of the teeth and the fœtus of the Australian group of pouched mammals—the marsupials—hasentirely upset previous notions, to the effect that these are a primitive group, and has shown that their possession of only one replacing tooth is a retention of one out of many such teeth (the germs of which are present), as in placental mammals; and further that many of these marsupials have the nourishing outgrowth of the fœtus called the placenta fairly well developed, so that they must be regarded as a degenerate side-branch of the placental mammals, and not as primitive forerunners of that dominant series.

Fig. 19.Photograph of the skull of a male Okapi—showing the paired boney horn-cores—similar to those of the Giraffe, but connected with the frontal bones and not with the parietals as the horn-cores of Giraffes are.

Photograph of the skull of a male Okapi—showing the paired boney horn-cores—similar to those of the Giraffe, but connected with the frontal bones and not with the parietals as the horn-cores of Giraffes are.

Fig. 20.Drawings by Professor Grassi, of Rome, of the young of the common Eel and its metamorphosis. All of the natural size. The uppermost figure represents a transparent glass-like creature—which was known as a rare “find” to marine naturalists, and received the nameLeptocephalus. Really it lives in vast numbers in great depths of the sea—five hundred fathoms and more. It is hatched here from the eggs of the common Eel which descends from the ponds, lakes, and rivers of Europe in order to breed in these great depths. The gradual change of theLeptocephalusinto a young Eel or “Elver” is shown, and was discovered by Grassi. The young Eels leave the great depth of the ocean and ascend the rivers in immense shoals of many hundred thousand individuals, and wriggle their way up banks and rocks into the small streams and pools of the continent.The above figures were published by Professor Grassi in November 1896, in theQuarterly Journal of Microscopical Science, edited by E. Ray Lankester and published by Churchill & Sons.

Drawings by Professor Grassi, of Rome, of the young of the common Eel and its metamorphosis. All of the natural size. The uppermost figure represents a transparent glass-like creature—which was known as a rare “find” to marine naturalists, and received the nameLeptocephalus. Really it lives in vast numbers in great depths of the sea—five hundred fathoms and more. It is hatched here from the eggs of the common Eel which descends from the ponds, lakes, and rivers of Europe in order to breed in these great depths. The gradual change of theLeptocephalusinto a young Eel or “Elver” is shown, and was discovered by Grassi. The young Eels leave the great depth of the ocean and ascend the rivers in immense shoals of many hundred thousand individuals, and wriggle their way up banks and rocks into the small streams and pools of the continent.The above figures were published by Professor Grassi in November 1896, in theQuarterly Journal of Microscopical Science, edited by E. Ray Lankester and published by Churchill & Sons.

The above figures were published by Professor Grassi in November 1896, in theQuarterly Journal of Microscopical Science, edited by E. Ray Lankester and published by Churchill & Sons.

Speculations as to the ancestral connection of the great group of vertebrates with other great groups have been varied and ingenious; but most naturalists are now inclined to the view that it is a mistake to assumeany such connection in the case of vertebrates of a more definite character than we admit in the case of starfishes, shell-fish, and insects. All these groups areultimately connected by very simple, remote, and not by proximate ancestors, with one another and with the ancestors of vertebrates.

Fig. 21.The unicellular parasiteBenedenia, from the gut of the common Poulp or Octopus. 1 is the normal male individual; 2 and 3 show stages in the production of spermatozoa on its surface by budding; 4, 5 and 6 show a female parasite with spermatozoa approaching it.

The unicellular parasiteBenedenia, from the gut of the common Poulp or Octopus. 1 is the normal male individual; 2 and 3 show stages in the production of spermatozoa on its surface by budding; 4, 5 and 6 show a female parasite with spermatozoa approaching it.

Fig. 22.Production of spermatozoa on the surface of the unicellular parasiteCoccidium oviforme, from the Rabbit’s intestines.

Production of spermatozoa on the surface of the unicellular parasiteCoccidium oviforme, from the Rabbit’s intestines.

The origin of the limbs of vertebrates is now generally agreed to be correctly indicated in the Thatcher-Mivart-Balfourtheory to the effect that they are derived from a pair of continuous lateral fins, in fish-like ancestors, similar in every way to the continuous median dorsal fin of fishes.

Fig. 23.Spermatozoa (often called “microgametes”) of the unicellular parasiteEchinosporafound in the gut of the small CentipedeLithobius mutabilis.

Spermatozoa (often called “microgametes”) of the unicellular parasiteEchinosporafound in the gut of the small CentipedeLithobius mutabilis.

The discovery of the formation of true spermatozoa by simple unicellular animals of the group Protozoa is a startling thing, for it had always been supposed that these peculiar reproductive elements were only formed by multicellular organisms (figs. 21,22, and23). They have been discovered in some of the gregarina-like animalcules, theCoccidia, and also in the blood-parasites.

Among plants one of the most important discoveries relates to these same reproductive elements, the spermatozoa, which by botanists are called antherozoids. A great difference between the whole higher series of plants, the flowering plants or phanerogams, and thecryptogams or lower plants, including ferns, mosses, and algae, was held to be that the latter produce vibratile spermatozoa like those of animals which swim in liquid and fertilise the motionless egg-cell of the plant. Two Japanese botanists (and the origin of this discovery from Japan, from the University of Tokio, in itself marks an era in the history of science), Hirase and Ikeno, astonished the botanical world fifteen years ago by showing that motile antherozoids or spermatozoa are produced by two gymnosperms, the ging-ko tree (orSalisburya) and the cycads (fig. 24). The pollen-tube, which is the fertilising agent in all other phanerogams, develops in these cone-bearing trees, beautiful motile spermatozoa, which swim in a cup of liquid provided for them in connection with the ovules. Thus a great distinction between phanerogams and cryptogams was broken down, and the actual nature of the pollen-tube as a potential parent of spermatozoids demonstrated.

Fig. 24.Spermatozoa (antherozoids) ofCycas revoluta, seen from the side and from above. The spermatozoon is spherical, carrying a spiral band of minute vibratile hairs (cilia) by which it is propelled.

Spermatozoa (antherozoids) ofCycas revoluta, seen from the side and from above. The spermatozoon is spherical, carrying a spiral band of minute vibratile hairs (cilia) by which it is propelled.

When we come to the results of the digging out and study of extinct plants and animals, the most remarkable results of all in regard to the affinities and pedigree of organisms have been obtained. Among plants the transition between cryptogams and phanerogamshas been practically bridged over by the discovery that certain fern-like plants of the Coal Measures—theCycadofilices, supposed to be true ferns, are really seed-bearing plants and not ferns at all, but phanerogams of a primitive type, allied to the cycads and gymnosperms. They have been re-christenedPteridospermsby Scott, who, together with F. Oliver and Seward, has been the chief discoverer in this most interesting field.

Fig. 25.The gigantic three-horned Reptile,Triceratops, as large as an Elephant, found in Jurassic strata in North America. A model of the skeleton may be seen in the Natural History Museum in London.

The gigantic three-horned Reptile,Triceratops, as large as an Elephant, found in Jurassic strata in North America. A model of the skeleton may be seen in the Natural History Museum in London.

By their fossil remains whole series of new genera of extinct mammals have been traced through the tertiary strata of North America and their genetic connections established; and from yet older strata of the same prolific source we have almost complete knowledge of several genera of huge extinctDinosauriaof great variety of form and habit (fig. 25).

Fig. 26.Photograph of the skeleton of a large carnivorous Reptile from Triassic strata in North Russia, discovered by Professor Amalitzky and named by him,Inostransevia. The head alone is two feet in length.

Photograph of the skeleton of a large carnivorous Reptile from Triassic strata in North Russia, discovered by Professor Amalitzky and named by him,Inostransevia. The head alone is two feet in length.

Fig. 27.Photographs of completed models of the Devonian fishDrepanaspis, from Devonian slates of North Germany, worked out by Professor Traquair. The models are in the Natural History Museum, London.

Photographs of completed models of the Devonian fishDrepanaspis, from Devonian slates of North Germany, worked out by Professor Traquair. The models are in the Natural History Museum, London.

Fig. 28.The oldest fossil fish known—discovered in the Upper Silurian strata of Scotland, and namedBirkeniaby Professor Traquair.

The oldest fossil fish known—discovered in the Upper Silurian strata of Scotland, and namedBirkeniaby Professor Traquair.

The discoveries by Seeley at the Cape, and by Amalitzky in North Russia of identical genera of Triassic reptiles, which in many respects resemble the Mammalia and constitute the groupTheromorpha, is also a prominent feature in the palæontology of the past twenty-five years (fig. 26). Nor must we forget the extraordinary Devonian and Silurian fishes discovered and described by Professor Traquair (figs. 27and28). The most important discovery of the kind of late years has been that of the Upper Eocene and Miocene Mammals of the Egyptian Fayum, excavated by the Egyptian Geological Survey and by Dr. Andrews of the Natural History Museum, who has described and figured the remains. They include a huge four-horned animal as big as a rhinoceros, but quite peculiar in its characters—theArisinoïtherium—and the ancestors of the elephants, a group which was abundant in Miocene and Pliocene times in Europe and Asia, and in still later times in America,and survives at the present day in its representatives the African and Indian elephant. One of the European extinct elephants—theTetrabelodon—had, we have long known, an immensely long lower jaw with large chisel-shaped terminal teeth. It had been suggested by me that the modern elephant’s trunk must have been derived from the soft upper jaw and nasal area, which rested on this elongated lower jaw, by the shortening (in the course of natural selection and modification by descent) of this long lower jaw, to the present small dimensions of the elephant’s lower jaw, and the consequent down-dropping of the unshortened upper jaw and lips, which thus become the proboscis. Dr. Andrews has described from Egypt and placed in the Museum in London specimens of two new genera—onePalæomastodon, in which there is a long, powerful jaw, an elongated face, and an increased number of molar teeth (seefigs. 29and30); the second,Meritherium(fig. 31), an animal with a hippopotamus-like head, comparatively minute tusks, and a well-developed complement of incisor, canine, and molar teeth, like a typical ungulate mammal. Undoubtedly we have in these two forms the indications of the steps by which the elephants have been evolved from ordinary-looking pig-like creatures of moderate size, devoid of trunk or tusks. Other remains belonging to this great mid-African Eocene fauna indicate that notonly the Elephants but the Sirenia (the Dugong and Manatee) took their origin in this area. Amongst them are also gigantic forms of Hyrax, like the little Syrian coney and many other new mammals and reptiles.

Fig. 29.Photograph of a complete model of the skull and lower jaw of the ancestral elephant,Palæomastodon, discovered by Dr. Andrews in the Upper Eocene of the Fayum Desert, Egypt, and modelled and restored under his direction in the Natural History Museum, London. The comparatively short trunk or snout rested on the broad front teeth of the long lower jaw. The face is elongated, and the cheek-teeth are numerous.

Photograph of a complete model of the skull and lower jaw of the ancestral elephant,Palæomastodon, discovered by Dr. Andrews in the Upper Eocene of the Fayum Desert, Egypt, and modelled and restored under his direction in the Natural History Museum, London. The comparatively short trunk or snout rested on the broad front teeth of the long lower jaw. The face is elongated, and the cheek-teeth are numerous.

Fig. 30.Photograph of the lower face of the skull of a specimen ofPalæomastodonbrought from Egypt in April, 1906, by Dr. Andrews, and now in the Natural History Museum, London. The six characteristic cheek-teeth on each side, and the pair of sabre-like tusks in front, are well seen.

Photograph of the lower face of the skull of a specimen ofPalæomastodonbrought from Egypt in April, 1906, by Dr. Andrews, and now in the Natural History Museum, London. The six characteristic cheek-teeth on each side, and the pair of sabre-like tusks in front, are well seen.

Fig. 31.Drawing of the skull and lower jaw of theMeritherium, discovered by Dr. Andrews in the Upper Eocene of the Fayum Desert. The shape of the skull and proportions of face and jaw are like those of an ordinary hoofed mammal such as the pig; but the cheek-teeth are similar to those of theMastodon, and whilst the full complement of teeth is present in the front of the upper jaw, we can distinguish the big tusk-like incisor which alone survives on each side inPalæomastodon,Mastodon, and the elephants, as the great pair of tusks.

Drawing of the skull and lower jaw of theMeritherium, discovered by Dr. Andrews in the Upper Eocene of the Fayum Desert. The shape of the skull and proportions of face and jaw are like those of an ordinary hoofed mammal such as the pig; but the cheek-teeth are similar to those of theMastodon, and whilst the full complement of teeth is present in the front of the upper jaw, we can distinguish the big tusk-like incisor which alone survives on each side inPalæomastodon,Mastodon, and the elephants, as the great pair of tusks.

Another great area of exploration and source of new things has been the southern part of Argentina and Patagonia, where Ameghino, Moreno, and Scott of Princeton have brought to light a wonderful series of extinct ant-eaters, armadilloes, huge sloths, and strange ungulates, reaching back into early Tertiary times. But most remarkable has been the discovery in this area of remains which indicate a former connection with theAustralian land surface. This connection is suggested by the discovery in the Santa Cruz strata, considered to be of early Tertiary date, of remains of a huge horned tortoise which is generically identical with one found fossil in the Australian area of later date, and known asMiolania. In the same wonderful area we have the discovery in a cave of the fresh bones, hairy skin, and dung of animals supposed to be extinct, viz., the giant sloth,Mylodon, and the peculiar horse,Onohippidium. These remains seem to belong to survivors from the last submergence of this strangely mobile land-surface, and it is not improbable that some individuals of this ‘extinct’ fauna are still living in Patagonia. The region is still unexplored and those who set out to examine it have, by some strange fatality, hitherto failed to carry out the professed purpose of their expeditions.

I cannot quit this immense field of gathered fact and growing generalisation without alluding to the study of animal embryology and the germ-layer theory, which has to some extent been superseded by the study of embryonic cell-lineage, so well pursued by some American microscopists. The great generalisation of the study of the germ-layers and their formation seems to be now firmly established—namely, that the earliest multicellular animals were possessed of one structural cavity, the enteron, surrounded by a double layer of cells, the ectoderm and endoderm. TheseEnterocœlaorCœlenteragave rise to forms having a second great body-cavity, the cœlom, which originated not as a split between the two layers, as was supposed twenty-five years ago by Haeckel and Gegenbaur and their pupils, but by a pouching of the enteron to form one or more cavities in which the reproductive cells should develop—pouchings which became nipped off from the cavity of theirorigin, and formed thus the independent cœlom. The animals so provided are theCœlomocœla(as opposed to theEnterocœla), and comprise all animals above the polyps, jelly-fish, corals, and sea-anemones. It has been established in these twenty-five years that the cœlom is a definite structural unit of the higher groups, and that outgrowths from it to the exterior (cœlomoducts) form the genital passages, and may become renal excretory organs also. The vascular system has not, as it was formerly supposed to have, any connection of origin with the cœlom, but is independent of it, in origin and development, as also are the primitive and superficial renal tubes known as nephridia. These general statements seem to me to cover the most important advance in the general morphology of animals which we owe to embryological research in the past quarter of a century.[16]

Before leaving the subject of animal morphology I must apologise for my inability to give space and time to a consideration of the growing and important science of anthropology, which ranges from the history of human institutions and language to the earliest prehistoric bones and implements. Let me therefore note here the discovery of the cranial dome ofPithecanthropusin a river gravel in Java—undoubtedly the most ape-like of human remains, and of great age (seefigs. 1 and 2); and, further, the Eoliths of Prestwich (seefigs. 3and4), in the human authorship of which I am inclined to believe, though I should be sorry to say the same of all the broken flints to which the name ‘Eolith’ has been applied. The systematic investigation and record of savage races have taken on a new and scientific character. Such work asBaldwin Spencer’s and Haddon’s in Australasia furnish examples of what is being done in this way.

Fig. 32.

Bacillus radicola, the parasite which infests the roots of leguminous plants and causes the growth of nodules whilst assisting the plant in the assimilation of nitrogen: (a) Nodule of the roots of the common Lupine, natural size; (b) longitudinal section through a Lupine root and nodule; (c) a single cell from a Lupine nodule showing the bacteria or bacilli, as black particles in the protoplasm, magnified 600 diameters; (d) bacilli from the root nodule of the Lupine; (e) triangular forms of the bacillus from the root nodules of the Vetch; (f) oval forms from the root nodules of the Lupine; (d e f) are magnified 1,500 diameters.

Physiology of Plants and Animals.—Since I have not space to do more than pick out the most important advances in each subject for brief mention, I must signalize in regard to the physiology of plants the better understanding of the function of leaf-green or chlorophyll due to Pringsheim and to the Russian Timiriaseff, the new facts as to the activity of stomata in transpiration discovered by Horace Brown, and the fixation of free nitrogen by living organisms in the soil and by organisms (Bacillus radicola) parasitic in the rootlets of leguminous plants (seefig. 32), which thus benefit by a supply of nitrogenous compounds which they can assimilate.

Great progress in the knowledge of the chemistry of the living cells or protoplasm of both plants and animals has been made by the discovery of the fact that ferments or enzymes are not only secreted externally by cells, but exist active and preformedinsidecells. Büchner’s final conquest of the secret of the yeast-cell by heroic mechanical methods—the actual grinding to powder of these already very minute bodies—first established this, and now successive discoveries of intracellular ferments have led to the conclusion that it is probable that the cell respires by means of a respiratory ‘oxydase,’ builds up new compounds and destroys existing ones, contracts and accomplishes its own internal life by ferments. Life thus (from the chemical point of view) becomes a chain of ferment actions. Another most significant advance in animal physiology has been the sequel (as it were) of Bernard’s discovery of the formation of glycogen in the liver, a substance not to be excreted, but to be taken up by the blood and lymph, and in many ways more important than the more obvious formation of bile which is thrown out of the gland into the alimentary canal. It has been discovered that many glands, such as the kidney and pancreas and the ductless glands, the suprarenals, thyroid, and others, secrete indispensable products into the blood and lymph. Hence myxœdema, exophthalmic goitre, Addison’s disease, and other disorders have been traced to a deficiency or excess of internal secretions from glands formerly regarded as interesting but unimportant vestigial structures. From these glands have in consequence been extracted remarkable substances on which their peculiar activity depends. From the suprarenals a substance has been extracted which causes activity of all those structures which the sympathetic nerve-system can excite to action; the thyroid yields a substance which influences the growth of the skin, hair, bones, &c.; the pituitary gland, an extract which is a specific urinary stimulant. Quite lately the mammalian ovary has been shown by Starling to yield a secretion which influences the state of nutrition of the uterus and mammæ. A great deal more might be said here on topics such as these—topics of almost infinite importance; but the fact is that the mere enumeration of the most important lines of progress in any one science would occupy many pages.

Fig. 33.The continuity of the protoplasmof neighbouring vegetable cells, bymeans of threads which perforate thecell-walls. Drawing (afterGardiner)of cells from the pulvinus ofRobinia.

The continuity of the protoplasmof neighbouring vegetable cells, bymeans of threads which perforate thecell-walls. Drawing (afterGardiner)of cells from the pulvinus ofRobinia.

Nerve-physiology has made immensely important advances. There is now good evidence that all excitation of one group of nerve-centres is accompanied by theconcurrent inhibitionof a whole series of groups of other centres, whose activity might interfere with that of the group excited to action. In a simple reflex flexure of the knee the motor-neurones to the flexor muscles are excited, but concurrently the motor-neurones to the extensor muscles are thrown into a state of inhibition, and so equally with all the varied excitations of the nervous system controlling the movements and activities of the entire body.

Fig. 34.Diagrammatic representation of the structures present in a typical cell (afterWilson). Note the two centrosomes, sometimes single.

Diagrammatic representation of the structures present in a typical cell (afterWilson). Note the two centrosomes, sometimes single.

The discovery of the continuity of the protoplasm through the walls of the vegetable cells by means of connectingcanals and threads (seefig. 33) is one of the most startling facts discovered in connection with plant-structure, since it was held twenty years ago that a fundamental distinction between animal and vegetable structure consisted in the boxing-up or encasement of each vegetable cell-unit in a case of cellulose, whereas animal cells were not so imprisoned, but freely communicated with one another. It perhaps is on this account the less surprising that lately something like sense-organs have been discovered on the roots, stems, and leaves of plants, which, like the otocysts of some animals, appear to be really ‘statocytes,’ and to exert a varying pressure according to the relations of these parts of the plant to gravity. There is apparently something resembling a perception of theincidence of gravity in plants which reacts on irritable tissues, and is the explanation of the phenomena of geotropism. These results have grown out of the observations of Charles Darwin, followed by those of F. Darwin, Haberlandt, and Nemec.

Fig. 35.—The Number of the Chromosomes: (a) Cell of the asexual generation of the cryptogamPellia epiphylla: the nucleus is about to divide, a polar ray-formation is present at each end of the spindle-shaped nucleus, the chromosomes have divided into two horizontal groups each of sixteen pieces:sixteenis the number of the chromosomes of the ordinary tissue cells ofPellia. (b) Cell of the sexual generation of the same plant (Pellia) in the same phase of division, but with thereducednumber of chromosomes—namely,eightin each half of the dividing nucleus. The completed cells of the sexual generation have onlyeightchromosomes. (c) Somatic or tissue cell of Salamander showingtwenty-four∨-shaped chromosomes, each of which is becoming longitudinally split as a preliminary to division. (d) Sperm-mother-cell from testis of Salamander, showing thereducednumber of chromosomes of the sexual cells—namely,twelve; each is split longitudinally. (From original drawings by Prof. Farmer and Mr. Moore.)

A few words must be said here as to the progress of our knowledge of cell-substance, and what used to be called the protoplasm question. We do not now regard protoplasm as a chemical expression, but, in accordance with von Mohl’s original use of the word, as a structure which holds in its meshes many and very varied chemical bodies of great complexity. Within these twenty-five years the ‘centrosome’ of the cell-protoplasm has been discovered (seefig. 34), and a great deal has been learnt as to the structure of the nucleus and its remarkable stain-taking bands, the chromosomes. We now know that these bands are of definite fixed number, varying in different species of plants and animals, and that they are halved in number in the reproductive elements—the spermatozoid and the ovum—so that on union of these two to form the fertilized ovum (the parent cell of all the tissues), the proper specific number is attained (seefigs. 35and36). It has been pretty clearly made out by cutting up large living cells—unicellular animals—that the body of the cell alone, without the nucleus, can do very little but move and maintain for a time its chemical status. But it is the nucleus which directs and determines all definite growth, movement, secretion, and reproduction. The simple protoplasm, deprived of its nucleus, cannot form a new nucleus—in fact, can do very little but exhibit irritability. I am inclined to agree with those who hold that there is not sufficient evidence that any organism exists at the present time which has not both protoplasm and nucleus—in fact,that the simplest form of life at present existing is a highly complicated structure—a nucleated cell. That does not imply that simpler forms of living matter have not preceded those which we know. We must assume that something more simple and homogeneous than the cell, with its differentiated cell-body or protoplasm, and its cell kernel or nucleus, has at one time existed. But the various supposed instances of the survival to the present day of such simple living things—described by Haeckel and others—have one by one yielded to improved methods of microscopic examination and proved to be differentiated into nuclear and extra-nuclear substance.

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