1968. Besides those substances which animals make use of as food, water is likewise employed as drink, and as the vehicle of nutritious matter. Salt is necessarily mixed with the drink of the inhabitants of the ocean, and is relished by man and many other animals. Other inorganic substances are likewise employed for a variety of purposes. Many savages make use of steatite and clay along with their food, The common earthworm swallows the soil, from which, in its passage through the intestines, it extracts its nourishment. 1969. In some cases, substances are swallowed for other purposes than nourishment. Stones are retained in the stomach of birds to assist in triturating the grain. The wolf is said to satisfy his hunger by filling his stomach with mud. SECT. II. Of the Circulating System. 1970. The food being reduced to a pultaceous mass, and mixed with a variety of secreted fluids, by means of the digestive organs, is in this state denominated chyme. This mixture exhibits a chemical constitution nearly approaching that of blood, into which it is destined to be converted, by the separation of the useless from the useful part. This is effected by certain vessels called lacteals, which absorb the nutritious part of the chyme, and convey it to a particular receptacle. Another set of absorbents, the lymphatics, take up all the substances which have been ejected from the circulation, and which are no longer necessary in the particular organs, and communicate their contents to the store already provided by the lacteals. The veins receive the altered blood from the extremities of the arteries or the glands, in which they terminate, and proceed with it towards the lungs, to be again aerated. In their progress they obtain the collected fluid of the other absorbents, and, in the lungs, again prepare the whole for the use of the system. Thus, during the continuance of life, the arteries supply the materials by which the system is invigorated and enlarged, and oppose that tendency to decay, produced by the influence of external objects. The process continues during the whole of life, new matter is daily added, while part of the old and useless is abstracted. The addition is greatest in early life, the abstraction is greatest in old age. 1971. This continued system of addition and subtraction has led some to conclude, that a change in the corporeal identity of the body takes place repeatedly during the continuance of life; that none of the particles of which it consisted in youth remain in its composition in old age. Some have considered the change effected every three, others every seven, years. This opinion, however, is rendered doubtful by many well known facts. Letters marked on the skin by a variety of substances frequently last for life. There are some diseases, such as small-pox and measles, of which the constitution is only once susceptible; but it is observed to be liable to the attack of these diseases at every period of human life. SECT. III. Of the Reproductive System of Animals. 1972. Animals are reproduced in consequence of the functions of certain organs, with the exception of some of the very lowest in the scale. In those animals which possess peculiar organs for ne preparation of the germ or ovum, some are androgynous (manwoman), and either have the sexual organs incorporated, and capable of generating without assistance, or the sexual organs are distinct, and the union of two individuals is necessary for impregnation: others have the sexual organs separate, and on different individuals. The young of such animals are either nourished at first by the store of food in the egg, or by the circulating juices of the mother. Those species in which the former arrangement prevails are termed oviparous, while the term viviparous is restricted to the latter. 1973. In all animals it is the business of the female to prepare the ovum or germ, and bring it to maturity. For this purpose, the germ is produced in the ovarium, farther perfected in the uterus or matrix, and finally expelled from the system through the vagina. The office of the male is to impregnate the germ by means of the spermatic fluid. This fluid is secreted in the testicles, transmitted by the spermatic ducts, and finally conveyed by the external organ to its ultimate destination. 1974. Among the viviparous animals, the reproductive organs present many points of resemblance, and appear to be constructed according to a common model. It is otherwise with the sexual organs of the oviparous tribes. These exhibit such remarkable differences in form and structure that it is impossible to collect them into natural groups, or assign to them characters which they have in common. 1975. The manner in which the eggs of birds are impregnated by the male has not been satisfactorily determined. With the exception of the cicatricula, a female bird, in the absence of the male, can produce an egg. The conjunction of the sexes, however, is necessary for the impregnation of the egg, and the effect is produced previous to the exclusion. 1976. În many kinds of fishes and reptiles, the yolks, after being furnished with their glair, are ejected from the body of the female, and the impregnating fluid from the male is afterwards poured over them. Impregnation can be effected readily in such cases, by the artificial application of the spermatic fluid. 1977. Impregnation in insects appears to take place while the eggs pass a reservoir containing the sperm, situated near the termination of the oviduct in the volva. 1978. The most simple mode of hatching is effected by the situation in which the eggs are placed by the mother, after or during their exclusion. In this mode a place is usually selected where the eggs will be exposed to a suitable and uniform temperature, and where a convenient supply of food may be easily obtained for the young animals. Such arrangements prevail in the insect tribe. 1979. In the second mode, the mother, aided in some cases by the sire, forms a nest, in which she deposits her eggs, and, sitting upon them, aids their hatching by the heat of her body. Birds in general hatch their young in this manner. 1980. In the third mode, the eggs are retained in the uterus, without any connection, however, by circulating vessels, until the period when they are ready to be hatched, when egg and young are expelled at the same time. This takes place in some sharks and Mollusca. The animals which exercise this last kind of incubation are termed ovoviviparous. In the Ràna pipa, the eggs are deposited in a bag on the back, where they are hatched, and where the young animals reside for some time after birth. Some animals, as the aphis, are oviparous at one season, and ovoviparous at another. 1981. The young, after being hatched, are, in many cases, independent of their parent, and do not stand 'n need of any assistance: they are born in the midst of plenty, and have organs adapted to the supply of heir wants. Thus, many insects are hatched on, or within the very leaves which they are afterwards to levour. In other cases, the young are able to follow their parents, and receive from them a supply of appropriate food; or, if unable to follow, their parents bring their food to the nests. 1982. The changes which the young of oviparous animals undergo in passing from infancy to maturity have long attracted the notice of the inquisitive observer. The egg of the frog is hatched in the water, and the young animal spends in that element a part of its youth. While there it is furnished with a tail and external bronchiæ; both of which are absorbed, and disappear, when it becomes an inhabitant of the land. The infancy of the butterfly is spent in the caterpillar state, with organs of motion and mastication which are peculiar to that period. It is destined to endure a second hatching, by becoming enveloped in a covering, and suffering a transformation of parts previously to appearing in its state of maturity. These metamorphoses of oviparous animals present an almost infinite variety of degrees of change, differing in character according to the tribes or genera. 1983. In birds, it is well known that one sexual union suffices for the production of impregnated eggs during the period of laying. This is a case somewhat analogous to those quadrupeds which produce several young at a birth with one impregnation, differing however, in the circumstance that the eggs are not all produced at the same time, although they are afterwards hatched by the same incubation. In the Aphides, or plant-lice, as they are called, one impregnation not only renders fertile the eggs of the individual, but the animals produced from these, and the eggs of those again, unto the ninth generation. 1984. Androgynous animals are of two kinds; those where impregnation takes place by the mutual application of the sexual organs of two individuals; and those where the hermaphroditism is complete. The Mollusca exhibit examples of both kinds. 1985. Gemmiparous animals are exemplified in the Hydra or fresh-water polypus, and other zoophytes. 1986. Hybridous animals. In the accomplishment of the important purpose of generation, it is observed, that, in the season of desire, individuals of a particular species are drawn together by mutual sympathy, and excited to action by a common propensity. The produce of a conjunction between individuals of the same species partakes of the characters common to the species, and exhibits in due time the characteristic marks of puberty and fertility. In a natural state, the selective attribute of the procreative instinct unerringly guides the individuals of a species towards each other, and a preventive aversion turns them with disgust from those of another kind. In a domesticated state, where numerous instincts are suppressed, and where others are fostered to excess, individuals belonging to different species are sometimes known to lay aside their natural aversion, and to unite in the business of propagation. Instances of this kind occur among quadrupeds, birds, and fishes, among viviparous and oviparous animals, where impregnation takes place within, as well as when it is effected without, the body. The product of such an unnatural union is termed a hybridous animal. The following circumstances appear to be connected with hybridous productions: 1987. The parents must belong to the same natural genus or family. There are no exceptions to this law. Where the species differ greatly in manners and structure, no constraints or habits of domestication will force the unnatural union. On the other hand, sexual union sometimes takes place among individuals of nearly related species. Thus, among quadrupeds, the mule is the produce of the union of the horse and the ass. The jackall and the wolf both breed with the dog. Among birds, the canary and goldfinch breed together, the Muscovy and common duck, and the pheasant and hen. Among fishes, the carp has been known to breed with the tench, the crusian, and even the trout. (Phil. Trans., 1771, p. 318) 1988. The parents must be in a confined or domesticated state. In all those hybridous productions which have yet been obtained, there is no example of individuals of one species giving a sexual preference to those of another. Among quadrupeds and birds, those individuals of different species which have united, have been confined and excluded from all intercourse with those of their own kind. In the case of hybridous fishes, the ponds in which they have been produced have been small and overstocked, and no natural proportion observed between the males and females of the different kinds. As the impregnating fluid, in such situations, is spread over the eggs after exclusion, a portion of it belonging to one species may have come in contact with the unimpregnated eggs of another species, by the accidental movements of the water, and not in consequence of any unnatural effort. In all cases of this unnatural union among birds or quadrupeds, a considerable degree of aversion is always exhibited, a circumstance which never occurs among individuals of the same species. 1989. The hybridous products are barren. The peculiar circumstances which are required to bring about a sexual union between individuals of different species sufficiently account for the total absence of hybridous productions in a wild state; and, as if to prevent even in a domesticated state the introduction and extension of spurious breeds, such hybridous animals, though in many cases disposed to sexual union, are incapable of breeding. There are, indeed, some statements which render it probable that hybrid animals have procreated with perfect ones; at the same time there are few which are above suspicion. 295 CHAP. V. Animal Pathology; or the Duration, Diseases, and Casualties of Animal Life. 1990. Each species of animal is destined, in the absence of disease and accidents, to enjoy existence during a particular period. In no species, however, is this term absolutely limited, as we find some individuals outliving others, by a considerable fraction of their whole lifetime. In order to find the ordinary duration of life of any species, therefore, we must take the average of the lives of a number of individuals, and rest satisfied with the approximation to truth which can thus be obtained. There is little resemblance in respect of longevity between the different classes, or even species, of animals. There is no peculiar structure, by which long-lived species may be distinguished from those that are short-lived. Many species whose structure is complicated live but for a few years, as the rabbit; while some of the testaceous Mollúsca, with more simple organisation, have a more extended existence. If longevity is not influenced by structure, neither is it modified by the size of the species. While the horse, greatly larger than the dog, lives to twice its age, man enjoys an existence three times longer than the former. 1991. The circumstances which regulate the term of existence in different species exhibit so many peculiarities, corresponding to each, that it is difficult to offer any general observations on the subject. Health is precarious, and the origin of diseases generally involved in obscurity. The condition of the organs of respiration and digestion, however, appears so intimately connected with the comfortable continuance of life, and the attainment of old age, that existence may be said to depend on the due exercise of the functions which they perform. Whether animals have their blood aerated by means of lungs or gills, they require a regular supply of oxygen gas: but as this gas is extensively consumed in the process of combustion, putrefaction, vegetation, and respiration, there is occasionally a deficiency in particular places for the supply of animal life. In general, where there is a deficiency of oxygen, there is also a quantity of carbonic acid or carburetted hydrogen present. These gases not only injure the system by occupying the place of the oxygen which is required, but exercise on many species a deleterious influence. To these circumstances may be referred the difficulty of preserving many fishes and aquatic Mollúsca in glass jars or small ponds; as a great deal of the oxygen in the air contained in the water is necessarily consumed by the germination and growth of the aquatic Cryptogàmia, and the respiration of the infusory Animálcula. In all cases, when the air of the atmosphere, or that which the water contains, is impregnated with noxious particles, many individuals of a particular species, living in the same district, suffer at the same time. The disease which is thus at first endemic or local, may, by being contagious, extend its ravages to other districts. 1902. The endemical and epidemical diseases which attack horses, sheep, and cows, obtain in this country the name of murrain, sometimes also that of the distemper. The general term, however, for the pestilential diseases with which these and other animals are infected, is Epizòöty (epi, amongst, zōon, an animal). 1993. The ravages which have been committed among the domesticated animals, at various times, in Europe, by epizootics, have been detailed by a variety of authors. Horses, sheep, cows, swine, poultry, fish, have all been subject to such attacks; and it has frequently happened, that the circumstances which have produced the disease in one species have likewise exercised a similar influence over others. That these diseases arise from the deranged functions of the respiratory organs, is rendered probable by the circumstance that numerous individuals, and even species, are affected at the same time; and this opinion is strengthened, when the rapidity with which they spread is taken into consideration. 1994. Many diseases, which greatly contribute to shorten life, take their rise from circumstances connected with the organs of digestion. Noxious food is frequently consumed by mistake, particularly by domesticated animals. When cows, which have been confined to the house during the winter season, and fed with straw, are turned out to the pastures in the spring, they eat indiscriminately every plant presented to them, and frequently fall victims to their imprudence. It is otherwise with animals in a wild state, whose instincts guard them from the common noxious substances of their ordinary situation. The shortening of life, in consequence of the derangement of the digestive organs, is chiefly produced by a scarcity of food. When the supply is not sufficient to nourish the body, it becomes lean, the fat being absorbed to supply the deficiency; feebleness is speedily exhibited, the cutaneous and intestinal animals rapidly multiply, and, in conjunction, accelerate the downfal of the system. 1995. The power of fasting, or of surviving without food, possessed by some animals, is astonishingly great. An eagle has been known to live five weeks without food; a badger a month; a dog thirty-six days; a toad fourteen months, and a beetle three years. This power of outliving scarcity for a time, is of signal use to many animals, whose food cannot be readily obtained; as is the case with beasts of prey and rapacious birds. But this faculty does not belong to such exclusively: wild pigeons have survived twelve days, an antelope twenty days, and a land tortoise eighteen months. Such fasting, however, is detrimental to the system, and can only be considered as one of those singular resources which may be employed in cases where, without it, life would speedily be extinguished. In situations where animals are deprived of their accustomed food, they frequently avoid the effects of starvation, by devouring substances to which their digestive organs are not adapted. Pigeons can be brought to feed on flesh, and hawks on bread. Sheep, when accidentally overwhelmed with snow, have been known to eat the wool off each other's backs. 1996. The various diseases to which animals are subject tend greatly to shorten the period of their existence. With the methods of cure employed by different species we are but little acquainted. Few accurate observations appear to have been made on the subject. Dogs frequently effect a cure of their sores by licking them. They eat grass to excite vomiting, and probably to cleanse their intestines from obstructions or worms, by its mechanical effects. Many land animals promote their health by bathing, others by rolling themselves in the dust. By the last operation, they probably get rid of the parasitical insects with which they are infested. 1997. But independently of scarcity, or disease, comparatively few animals live to the ordinary term of natural death. There is a wasteful war every where raging in the animal kingdom. Tribe is divided against tribe, and species against species, and neutrality is nowhere respected. Those which are preyed upon have certain means which they employ to avoid the foe; but the rapacious are likewise qualified for the pursuit. The exercise of the feelings of benevolence may induce us to confine our attention to the former, and adore that goodness which gives shelter to the defenceless, and protection to the weak, while we may be disposed to turn precipitately from viewing the latter, lest we discover marks of cruelty, where we wished to contemplate nothing but kindness. But we should recollect, that, to the lower animals, destitute as they are of the means of attending to the aged or diseased, sudden death is a merciful substitute for the lingering tortures of starvation. CHAP. VI. On the Distribution of Animals. 1998. On a superficial view, vegetables seem more abundant than animals: so contrary, however, is this to fact, that the species of animals, when compared with those of plants, may be considered in the proportion of 10 to 1. Hence it follows that botany, when compared with zoology, is a very limited study: plants, when considered in relation to insects alone, bear no proportion in the number of the species. The phanerogamous plants of Britain have been estimated in round numbers at 1500, while the insects that have already been discovered in this country (and probably many hundreds still remain unknown) amount to 10,000, which is more than six insects to one plant. It is therefore obvious that the knowledge acquired on the geographical distribution of animals, in comparison with what is known of plants, is slight and unsatisfactory: it is likewise attended with difficulties inseparable from the nature of beings so numerous and diversified, and which will always render it comparatively imperfect. It rarely happens that a single specimen of a plant is found isolated; the botanist can therefore immediately arrive at certain conclusions: if he is in a mountainous country, he is enabled to trace, without much difficulty, the lowest and the highest elevation at which a particular species is found; and the nature of the soil, which may be considered the food of the plant, is at once known. But these advantages do not attend the zoologist: his business is with beings perpetually moving upon the earth, or hid in the depths of ocean, performing numerous functions in secret; while of the marine tribes he can never hope to be acquainted with more than a very insignificant portion. The following observations must therefore be considered as merely an outline of those general laws which seem to regulate the geography of animals. 1999. The distribution of animals on the face of the globe must be considered under two heads, general and particular. The first relates to families or groups inhabiting particular zones, and to others by which they are represented in another hemisphere. The second refers to the local distribution of the animals of any particular country, or to that of individual species. It is to the general distribution of groups, as a celebrated writer has well observed, that the philosophic zoologist should first direct his attention, rather than to the locality of species. By studying nature in her higher groups, we discover that certain functions are developed under different forms, and we begin to discern something of the great plan of providence in the creation of animals, and arrive at general results, which must be for ever hid from those who limit their views to the habitations of species, or to the local distribution of animals. Fabricius, 2000. Animals, like plants, are generally found to be distributed in zones. in speaking of insects, divides the globe into eight climates, which he denominates the Indian, Egyptian, southern, Mediterranean, northern, oriental, occidental, and alpine. In the first he includes the tropics; in the second, the northern region immediately adjacent; in the third, the southern; in the fourth, the countries bordering on the Medi terrancan Sea, including also Armenia and Media; in the fifth, the northern part of Europe, interjacent between Lapland and Paris; in the sixth, the northern part of Asia, where the cold in winter is intense; in the seventh, North America, Japan, and China; and in the eighth, all those mountains whose summits are covered with eternal snow. It is, however, easy to perceive, that this, though a very ingenious, is a very artificial theory: the divisions are vague and arbitrary, and we know that animals of one country differ essentially from those of another, although both may enjoy the same degree of temperature. M. Latreille has therefore attempted a more definite theory. His two primary divisions are the arctic and antarctic climates, according to their situation above or below the equinoctial line; and taking twelve degrees of latitude for each climate, he subdivides the whole into twelve. Beginning at 84° N. L., he has seven arctic climates: viz. the polar, subpolar, superior, intermediate, supratropical, tropical, and equatorial: but his antarctic climates, as no land has been discovered below 60° S. L., amount only to five, beginning with the equatorial, and terminating with the superior. He proposes also a further division of subclimates, by means of certain meridian lines; separating thus the old world from the new, and subdividing the former into two great portions; an eastern, beginning with India; and a western, terminating with Persia. He proposes, further, that each climate should be considered as having 24° of longitude and 12° of latitude. This system certainly approximates more to what we see in nature than that proposed by Fabricius, yet Mr. Kirby observes with truth, that the division of the globe into climates by equivalent parallels and meridians wears the appearance of an artificial and arbitrary system, rather than of one according to nature. 2001. Mr. Swainson considers that the geographic distribution of animals is intimately connected with the limits of those grand and obvious sections into which the globe is divided; and that in proportion to the geographical proximity of one continent to another, so will be either the proportional identity or the analogy of their respective animals. He considers Europe, Asia, and Africa as agreeing more particularly in possessing certain animals in common, which seem excluded altogether from America and Australia; both of which are not only isolated in situation, but their animals have a decided difference of form and habit from those of the three continents of the old world. He considers that the animal geography of Asia is connected with that of Australia by the intervention of Borneo, New Guinea, and the neighbouring isles; while that of America unites with Europe towards the polar regions. These five great types or divisions will, of course, present certain affinities or analogies dependent upon other causes, arising from temperature, food, and locality. (Swainson's MSS.) 2002. Vertebrated animals have a wider range than invertebrated animals, thus resembling man, who is spread over the whole earth: the dog and the crow are found wild in almost every climate; the swallow traverses, in a few days, from the temperate to the torrid zone; and numerous other birds annually perform long migrations. Next to these, insects, above all the other Invertebratæ, enjoy the widest range; the house fly of America and of Europe are precisely the same; and Mr. Swainson has observed in Brazil vast flocks of butterflies, which annually migrate from the interior towards the coast. 2003 Marine animals have, in general, a wider range than those strictly terrestrial. This may probably originate in their being more independent of the effects of temperature. It is remarkable, that, with the exception of the crow and two or three others, the land birds of America differ entirely from those of Europe, yet that nearly all our aquatic species are found both in the new world and in the southern coasts of Africa. 2004. Subordinate to the five geographic groups already noticed, temperature may be considered the principal regulator of the station of animals; it has likewise a remarkable influence on their clothing. Many quadrupeds, inhabiting the colder regions, appear in their natural colours during summer, but become white in winter. The same change takes place in the plumage of several land birds; but is not observable in insects, or the cther invertebrate groups. Temperature has likewise a great influence on the size and colour of animals. The Sphinx convólvuli of Europe is found also in India, but of a much smaller size and more distinctly coloured: this is usually the effect of heat upon animals whose chief range is in temperate latitudes. On those which may be considered intertropical, a greater degree of heat not only increases the brilliancy of their colours, but adds to their size. There are many birds and insects common both to central Brazil and Cayenne; but from the greater heat of the latter country, the specimens are always larger and their plumage more beautiful. Temperature likewise affects the clothing of animals in respect both to quality and quantity. This is more particularly observed in such domesticated animals as have been transplanted from their natural climates. The covering of swine in warm countries consists of bristles of the same form and texture, thinly dispersed; while the same animals in colder climates have an additional coating of fine frizzled wool next the skin, over which the long bristly hairs project. This difference is very remarkable in the swine of northern Europe and |