In the last chapter we looked at a few of the interesting generalisations which have emerged of late years from the study of plant distribution. An enormous amount of detailed investigation had been done before these generalisations were arrived at, and though still much remains to be done, yet the broad lines of a science of plant distribution may now be said to be established. The scientific study of animal distribution has not yet reached a corresponding stage of advancement, partly no doubt because the dependence of the more highly organised and active animal upon the physical conditions is less close than that of the stationary plant, so that the subject is more difficult. Facts are accumulating on all sides, but the subject is still rather at the level of collecting information than at that of laying down broad generalisations. There are, however, indications of progress in many directions, and an attempt will be made here to suggest some of the lines along which research is especially busy at the present time.

In speaking of plants we confined our attention exclusively to land plants, for the reason that aquatic plants are usually small in size, relatively simple in structure, of somewhat limited vertical distribution, owing to their dependence upon light, and of little direct importance to man. In considering animals, on the other hand, we cannot exclude the aquatic forms, which are often of great human importance. In many regions man depends largely, sometimes even exclusively, on the animals of the sea for his food. We shall, then, begin with some account of aquatic animals, considering the subject, as before, especially from the point of view of the inhabitants of Europe and North America.

Beginning with the sea we find that the scientific study of marine animals received an enormous impetus from the work of the Challenger expedition. The results of that expedition appeared in many large volumes, which form a conspicuous feature in any complete scientific library and contain a mass of useful material. The Challenger expedition was followed by many others, European and American, and the result is that we now know a great deal about marine animals and their distribution. Further, the Fishery Boards of various Governments carry on continuous observations on the conditions of life in the seas near their coasts, which have added and are adding enormously to our knowledge.

We cannot here consider in detail the various facts brought to light by these means. Only a few general points can be touched upon. One interesting generalisation is that the life of the ocean can be divided into three groups: the life of the littoral or shore zone, the life of the open ocean (pelagic fauna), and the life of the great ocean depths (abyssal fauna). The last, though of great zoological interest, is so remote from human life that we need not consider it. The pelagic forms include both the small delicate organisms which float passively with the ocean currents, and also powerful swimmers like many fish, and aquatic mammals such as whales and seals. The littoral forms live in the region which is within the reach of land influences, that is, from low-tide mark to the edge of the Continental Shelf (cf. p. 27). Among forms directly important to man they include many fish; crustaceans such as crabs and lobsters; shell-fish such as oysters, mussels, clams, etc.; less important forms such as sea-urchins, which are extensively eaten in the Mediterranean; sponges, an important article of commerce; the various corals, especially the precious coral, and so on.

Of the useful marine animals, those which are most readily captured are the littoral forms, many of which, on shores where the tides are well marked, are exposed, or at least brought within easy reach, by the daily ebb and flow of the tide, and can be obtained with the minimum of apparatus. The extensive shell-mounds found on many shores, e. g. on those of Denmark, show at how early a date man availed himself of the abundant food supply to be obtained on the shore rocks. All edible animals found in the sea are “fish” to maritime populations, but fish in the restricted sense are usually more active, and require more skill for their capture than the less intelligent molluscs or crustaceans, and were probably not used at so early a date. They are by no means equally distributed in all seas, and their distribution shows many points of interest.

We must notice, in the first instance, that the waste of the land is of great importance in feeding marine forms, whether directly or indirectly. Marine animals, therefore, occur most abundantly over the Continental Shelf, where they are within reach of the food brought down by the rivers from the land. Again, many fish, or the organisms upon which fish feed, depend largely upon those minute plants called diatoms which float in the upper layers of the waters of the ocean. These are especially abundant in the colder seas, which doubtless helps to explain the abundance of fish in high latitudes. These diatoms, like many other small organisms in the sea, are swept about by the ocean currents, whose course greatly influences the movements of fish.

We saw in the case of forests that hot climates conduce to a great variety of species, while in colder climates the species are few, but the number of individuals very great. Something of the same sort seems to occur with fishes. In warm seas the number of species is very great, while in colder seas there are fewer species, but those which do occur are sometimes found in vast numbers. Fortunately for man these prolific northern species are often edible, whereas in warm seas poisonous or inedible forms are common. The valuable cod family is found chiefly in high latitudes.

The consequence of the facts just described is that valuable fisheries tend to occur in cool or cold climates rather than hot ones, and because of the dependence of so many forms on the Continental Shelf, they occur in the northern or land hemisphere rather than in the southern or oceanic one.

The most valuable fisheries in the world seem to be those off Newfoundland, where the broad Continental Shelf, forming the so-called “banks,” feeds myriads of cod. The mingling of the waters brought by the cold Labrador currents with those brought by the warm Gulf Stream perhaps influences this marvellous abundance of fish, as does also the waste brought by the icebergs.

Next to the banks of Newfoundland the most valuable fishing ground is the shallow North Sea, which, as we have seen, lies on the surface of the Continental Shelf. Fish are much more abundant here than on the narrower shelf on the western coast of Britain, and the wealth of the North Sea has been an important factor in the development of the countries bordering it.

The warm, salt, relatively deep, and tide-less Mediterranean is not nearly so rich in food fishes as the more northerly seas, a fact reflected in the large importation of dried fish alike from Newfoundland and from the region of the North Sea. But this is an economic and not a zoological statement, for the Mediterranean is in reality richer in fish species than the North Sea, in this respect, as in some others, approaching tropical regions. Among the economically important fish are the tunny, a very large form allied to the mackerel, which is dried, and sardines and anchovies, which are preserved in oil. Otherwise the fish are eaten fresh, and do not enter into general trade.

Fresh-water fish are abundant all over Europe, but with some exceptions they are not greatly prized in those countries where the better-flavoured marine fish can be obtained. Elsewhere, as in Russia, Germany, and parts of France, they become important.

Much more valuable than fresh-water fish in the strict sense are the various kinds of salmon, which come up the rivers to breed, but spend much time also in salt water. In the rivers of Scotland and Scandinavia salmon are still very important, but the fisheries in both cases are insignificant when compared with those of western North America. Salmon are inhabitants of temperate waters, and in North America do not extend further south than the rivers flowing into the north of the Gulf of California. Off the coast of Alaska and British Columbia, especially the former, they are enormously abundant, and being caught in quantities which far exceed the local demand are largely canned for export.

It is interesting to note that in regard to fresh-water fish, as with marine forms, the northern part of the world is especially rich in edible species, as compared alike with the southern hemisphere and with the tropics. The salmon family is confined to the northern hemisphere, and the carp family, though not peculiar, is largely represented in the north. To it belong the whitefish, which form important food fish in many parts of America. Sturgeon, which are important in Russia, occur in the great rivers of eastern Europe, and in parts of Asia, and also on the eastern coast of North America, and off California.

Turning next to the distribution of land animals within the European area, the first point is to note that for the globe at large zoologists employ zoogeographical divisions based chiefly upon the distribution of the land mammals. The reasons for this are manifold.

In the first place, mammals are of relatively recent origin, and in taking account of their spread over the globe, we may assume that in broad outline the continents, or at least the deep oceans, were much the same when the existing mammals were evolved as at present. This naturally simplifies the problem, for if we divided the globe into regions on the basis of the distribution of reptiles, for example, we should find it necessary to take account of many differences between the world in which the first reptiles arose and the world as it is at present.

Again, the chances of land mammals passing from one region to another, except by the crossing of land surfaces, are small. Thus the occurrence of similar land mammals in two regions now widely separated is almost certain proof of a former land connection between the two regions. The difficulty which most land mammals find in crossing mountain chains, or deserts, or considerable extents of water, makes it easy to define zoogeographical regions separated from one another by the existence of such “barriers to distribution” as they are called. Finally, mammals are highly organised animals of relatively large size, and their distribution is more easily studied than that of insects, for instance.

Without going into the zoogeographical regions in detail, we may note that there is, as already stated, considerable resemblance between the mammals of Europe, Asia, Africa and North America, that is, of the land hemisphere, while South America, which was for long isolated from North America, has a peculiar and relatively primitive fauna, and Australia, whose isolation has lasted longer, has an even more peculiar and a much more primitive fauna.

When we look at the fauna of the great land mass formed by the continents of Europe, Asia, Africa and North America, sometimes called by zoogeographers the ArctogÆic realm, we find that North America differs from the eastern land mass as regards its land mammals in several respects. Though long separated from South America it has been connected long enough for some of the southern forms to find their way northwards, so that we find skunks, raccoons, and other mammals strikingly different from analogous forms found in the Old World. Again, it is relatively so long since there was any free communication between the eastern and western hemispheres that the two faunas have had time to diverge without destroying the fundamental resemblance.

Beginning with the fauna of the Old World, we find that no effective barrier of any sort separates the animals of Europe, even of western Europe, from the animals of temperate Asia, even of eastern Asia. Right across from the British Isles to Japan, through about a hundred and fifty degrees of longitude, there is great general similarity in the land animals. To the south, on the other hand, the Atlas mountains and the African desert cut off the greater part of the continent of Africa, and eastwards the transverse mountain chains, no less than the difference of climate and the cold, barren nature of the uplands of central Asia, cut off the rich fauna of the peninsula of India with Further India, etc., from the habitable regions of temperate Asia, with their scantier fauna.

We are thus left with the conception of a very large and tolerably uniform zoological region, stretching right across Europe and temperate and northern Asia. This is the PalÆarctic region of zoogeographers.

The European section of it is somewhat impoverished as compared with the Asiatic section, partly perhaps because of the effects of the ice, and certainly also because for long ages Europe has been densely populated, and the larger wild animals have thus been exterminated. Asia, with its northern forests and its more southerly steppes, has always been a great reservoir of life, which has periodically overflowed into Europe. Some of these overflowing animals, like the black and the brown rats, succeeded in establishing themselves very firmly; others, like the saiga antelope, died out rapidly except in the extreme east of the European area.

It is possible that further investigation will show that not the mammals only, but land animals in general can be grouped according to their habitat like plants, but so far the attempts made in this direction have been tentative only. Generally, we may say that the mammals of Central Europe are of the woodland type, but no detailed classification into steppe and woodland animals exists. It may be useful, therefore, to indicate the chief kinds of mammals found in the European area, grouped according to affinity, in the absence of a geographical classification.

Mammals, apart from the egg-laying monotremes, and the marsupials of Australia, are divided into nine orders, and of these, one, that including the anteaters, etc., of South America, Africa and India, is entirely unrepresented in Europe. Another, the Cetaceans, or whales, has no land representatives; and the same is true of the aberrant sea-cows, though their ancestors lived on land and occurred in Egypt.

Excluding these orders we are left with six which have European representatives. These are the following:—

Primates, or monkeys and apes.

Insectivores, or insect-eating mammals, such as moles, shrews and hedgehogs.

Chiroptera, or bats.

Ungulates, or hoofed animals, including horses, cattle, sheep, deer, pigs, etc.

Carnivores, or flesh-eaters, including lions, cats, foxes, dogs, etc.

Rodents, or gnawing animals, among which are rats, mice, squirrels, etc.

The Primates are represented by one form only, the Barbary ape, found in Gibraltar. Bats are numerous, but are of less geographical interest than land forms. The remaining four orders are all important. The Ungulates include the largest land mammals, and their size and conspicuous nature have led to the gradual replacement of the wild forms by domesticated ones. Only a very few, such as deer, wild goats (ibex), the wild boar, the wild sheep (moufflon) of Corsica, manage to survive, and that mostly by aid of special protection. The presence of the large wild forms is incompatible with almost any form of agriculture as is often proved disastrously in Africa, hence man’s ruthless warfare upon them.

But if man has destroyed the large ungulates he has found himself unable even to reduce the numbers of the Rodents, who gain in many ways by civilisation. The destruction of their rivals, the grass-eating ungulates, increases their natural food-supply. In South America, where there were very few ungulates till the white man brought his flocks and herds, the rodents were very numerous and reached a great size. Again, the operations of agriculture give the rodents enormous artificial sources of food-supply, and the number of man’s domesticated or semi-domesticated animals makes him wage a bitter war against the small carnivores, the natural enemies of the rodents. Protected from their enemies, abundantly fed by man’s providence, it is no wonder that these small animals have multiplied greatly.

Their multiplication has been assisted by the fact that they inherit from their early days, when the struggle was keen, an enormous fertility. Many of the rodents are steppe animals, and share with steppe organisms in general the power of periodic multiplication in enormous numbers.

The steppe is a region where the rainfall is normally just enough to ensure a free growth of grass at certain seasons. Variations in rainfall, which perhaps occur in great cycles, may at one time produce a luxuriance of growth which increases the food-supply all round, and at another give rise to semi-desert conditions with a resulting enormous death-rate. The steppe organisms, then, must be very fertile because of the risks of their environment, and the Asiatic overflow is possibly determined by successions of years of abundant rainfall, which increase the number of individuals, followed by a series of years of scanty rain, which make it necessary for the overflow of population to migrate.

Among examples of European rodents we may mention the very destructive rats, mice and voles, which practically feed everywhere at man’s expense; and the hamster, an Asiatic form which reaches as far west as the Rhine, and stores large quantities of corn and other food in an elaborately made burrow. The hamster has the rodent power of rapid multiplication, and is often terribly destructive to cultivated crops. Rabbits are similarly very destructive where special precautions are not taken. Even the porcupine of southern Europe is capable of doing considerable damage. Less serious enemies of man are such forms as the following:—lemmings; marmots, of which there are two forms, an Alpine and an Asiatic, the latter extending like the other steppe animals into the plains of central Europe; beavers; squirrels; dormice; etc. These examples may be sufficient to illustrate the important points in regard to the rodents—their destructiveness, their fertility, and the fact that many were originally inhabitants of steppes and open plains, but tend, as man clears the forest-land for his own purposes, to extend their range to the cleared land, and to appropriate the new and extensive food-supply furnished by man’s industry.

While the ungulates, because of the nature of their food, must almost necessarily be rather large animals, the carnivores occur both in large and small forms. The tendency is for the large forms to be killed out with the progress of civilisation; thus the lion has wholly disappeared from Europe, wolf and bear are almost gone, but a considerable number of smaller forms still remain, such as badger, genet, wolverene, lynx, wild cat, stoat, marten, weasel, etc. The last order to be mentioned, that of the Insectivores, includes small mammals, such as moles, shrews, and hedgehogs, which feed largely on insects, but may be partially vegetarians.

As was to be expected from the climate and from the peculiar flora, the Mediterranean region possesses a richer fauna than central Europe, both as regards mammals and lower forms. Even the European portion shows considerable African influence.

A few words must be said about other land animals apart from mammals. In regard to birds it is noticeable that the habit of migration, and the fact that the greater part of the continent of Europe lies on the direct line between the northern breeding grounds of many species and the southern winter quarters, gives Europe a very rich bird fauna. The British Islands owe to their peculiarly mild climate a rich bird fauna at all seasons, for while the summer climate attracts many forms for nesting purposes, the mild winter brings many migrants flying from the cold of continental Europe.

In regard to birds as well as to other animals, the Mediterranean owes to its warm climate a richer fauna than countries farther north. Some interesting southern forms, such as pelican, flamingo and ibis, reach this region, though not extending into central Europe, except as stragglers.

The climate of Europe is not hot enough anywhere to lead to the presence of a rich reptilian fauna, but there is, again, a marked increase to the south. It is stated that there are only twenty-one species of reptiles in central Europe, while there are fifty-nine in southern Europe, and no less than a hundred and forty in the Mediterranean region taken in the large sense. Poisonous forms are few, and do not, as in hotter countries, constitute a serious menace to man. Very interesting is the presence of the chameleon in southern Spain, as in north Africa.

Perhaps the most important human aspect of the European reptiles is the presence of numbers of insect-eating forms. In the warmer parts of Europe every wall or patch of rock seems alive with lizards in the summer sunshine, and these must play a not inconsiderable part in the keeping down of noxious insects.

Omitting a great number of other groups, we may say something about insects, which are of enormous importance in human life, both directly and indirectly.

It has been shown of late years that many insects are the sole means by which certain very deadly diseases are transmitted from man to man, or from one animal to another. Almost every few months a new announcement of an insect-carried disease is made, but the most important forms are the following:—Mosquitoes and gnats transmit such diseases as malaria, yellow fever, and more horrible diseases still, due to the presence in the blood of small parasitic worms. Tsetse flies carry sleeping sickness, and also transmit the very fatal fly disease of domesticated animals, a fact which has been and is of great importance in the settlement of Africa. In the case of most diseases there seems to be a close connection between one particular species of insect and a particular disease.

Mosquitoes and gnats are very abundant in many parts of Europe, and the forms belonging to the genus Anopheles, which carry the germ of malaria, are widely distributed. In parts of the Mediterranean area their presence is associated with the prevalence of malaria, which has existed there for a prolonged period, and is believed by some to have had an important bearing upon the fates of the ancient civilisations of the Mediterranean basin.

The regions in Europe affected, or seriously affected, by malaria are diminishing yearly. This is now due to conscious efforts, but a similar process has been going on probably for a long period, for many obscure diseases, notably “ague,” seem to have been forms of malaria. Their disappearance seems to be due to drainage, which diminishes the breeding places of the mosquitoes, and also to the progress of agriculture, for ponds which form on rich, well-manured land are apparently unsuited to mosquito larvÆ. The subject is of great geographical importance, for the spread of man over the surface of the globe, and the progress of civilisation must have been influenced in all time by the prevalence of fly-borne disease. Such diseases have hitherto been the greatest obstacle in the way of the civilisation of Africa.

In Uganda extensive tracts of fertile wooded land have had to be abandoned on account of the presence there of the tsetse fly, while, prior to this abandonment, there were districts in which every living soul had been destroyed by the deadly sleeping sickness transmitted by this fly. We can hardly suppose that such facts are without a parallel in human history; and man’s distribution over the surface of the globe, and in detail the distribution of his settlements within a country, have doubtless been greatly influenced by the distribution even of such insignificant creatures as the various kinds of flies.

Even apart from their power of transmitting disease, the blood-sucking flies must have influenced man in his choice of localities for settlements, and must have been an important factor in the process of adjustment to his surroundings. The naturalist Brehm gives an appalling picture of the number and blood-thirstiness of the mosquitoes of the Siberian tundra, which render life almost intolerable there for both man and beast in summer. Even within the British Islands the uncultivated and undrained regions are often badly infested with small blood-sucking flies, and their numbers must have been vastly greater in the old days before drainage and intensive cultivation had reduced them. It is quite possible that some of the anomalies in regard to the spread of particular races of men over the surface can be explained by the varying susceptibility of different races to insect attack, and there can be no doubt that the blood-sucking insects must have had some effect in determining the rapidity or slowness with which particular tracts were colonised by man.

Apart from the blood-sucking flies, there are many other interesting points about the insects of Europe, notably the wealth of beautiful and striking forms which occur round the Mediterranean basin. One of these, which extends northwards and westwards to northern France, is the curious Praying Mantis, a predatory insect belonging to the same order as the locust. It is an eastern form, which, like so many others, has taken advantage of the mild climate of western Europe to extend its range far beyond what we must regard as its natural limits. In France it shows the effect of relatively unfavourable conditions in the fact that it takes some nine to ten months for the eggs to hatch, whereas in hotter countries the process may take place in a few weeks.

In the warmer parts of Europe a very striking feature is the number and large size of the members of the locust and grasshopper families, whose shrill noise is so characteristic a sound in, for example, the pastures of Switzerland in summer-time. Among the locusts there occur, in many parts of Europe, those migratory forms which possess that power of periodic enormous multiplication which we have already noted so frequently among grassland animals. The migratory instinct only seems to develop when the numbers have greatly increased in any given locality, and in Europe generally the climate does not permit this to take place. It does, however, occur in the south-east of the Mediterranean basin, notably in the island of Cyprus, in Syria, and also in Northern Africa, where locusts sometimes reach the dimensions of a plague.

We may add to this account of land animals a few details on the land mammals of North America. The great point of contrast here is that Europe, from the beginning of the historic period, has always been a relatively well-peopled region, while in America, prior to the advent of the white man, the population was scanty. There was thus far more room in North America than in Europe for great flocks of large mammals. Thus the plains and prairies carried great herds of bison, while to the north there were other herds of reindeer, which were never tamed by the inhabitants of North America as they were in the Old World by the Lapps and others. The musk-ox is another interesting animal found in the north of America. It once also lived in Europe, but died out long ago. Just as the coniferous forest and tundra in Asia produce many small fur-bearing animals, so do the forest and tundra of North America. Deer are present as in the Old World, though they are of different types, and there is a curious animal known as the prong-buck which is peculiar. Wild sheep occur as they do in Europe, but no wild horse nor ass roams the plains of America as they roam to-day the wastes of Asia. Without going into further detail, we may say generally that as regards wild animals, no less than as regards wild plants, North America shows a closer resemblance to Asia than to that favoured peninsula of Asia which the geographers call Europe.