PHILOSOPHY

OF

ZOOLOGY:

A GENERAL VIEW OF THE

STRUCTURE, FUNCTIONS, AND CLASSIFICATION OF ANIMALS.

ec. By JOHN FLEMING, D. D.

MINISTER OF FLISK, FIFESHIRE,

FELLOW OF THE ROYAL SOCIETY OF EDINBURGH, OF FTHE WERNERIAN

NATURAL HISTORY SOCIETY, &c.

IN TWO VOLUMES. cy

WITH ENGRA VINGS.

VOL. Il.

EDINBURGH : PRINTED FOR ARCHIBALD CONSTABLE & CO. EDINBURGH:

AND HURST, ROBINSON & CO. LONDON,

1822.

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THE

PHILOSOPHY

ZOOLOGY.

| ee observations which we have ventured to offer m the former volume, relate to what may be termed the Motive, the Sentient, the Nutritive, and Reproductive Functions of Animals. The various Organs of the animal frame have been described, their actions investigated, and the import- ant purposes of life, to which they are subservient, have at the same time been pointed ovt- An equally extensive field of Zoological Science remains to be investigated. Animals ave related to one another, and to the objects which surround them, in such a manner, as to be dependent on a variety of circumstances for the preservation of their éxistence, their dispersion over the globe, and their power of accommodation to the changes of the seasons. They are likewise to be viewed as admitting of division into classes and subordinate groups, according to the external or internal characters which they exhibit. In the investi- gation of these characters, a variety of methods are em- VOL. IT. , A

2 p PHILOSOPHY OF ZOOLOGY. ployed, and many rules have been prescribed, to regulate the principles of zoological nomenclature.

In order to enter more fully into these important sub- jects, we shall distribute the present volume into Four Parts. In the first, we shall consider the Condition of Animals in reference to their Duration, Distribution, and Economical Uses. In the second, we shall treat of the Methods of Investigation employed to ascertain their struc- ture and actions. In the third, we shall examine the Rules of Nomenclature ; while the fourth will embrace a Gene- ral View of the Classification of the Objects of the Ani- mal Kingdom. |

PART FIRST.

ON THE CONDITION OF ANIMALS.

CHAP. I.

ON THE DURATION OF ANIMALS.

mh

Pics species of Animal is destined, in the absence of disease and accidents, to enjoy existence during a particu- lar period. In no species, however, is this term absolutely limited, as we find some individuals outhiving others, by a considerable fraction of their whole hfe. In order to find the ordinary duration of life of any species, therefore, we

DURATION OF ANIMALS.

C2.

must take the average of the lives of a number of indivi- duals, and rest satisfied with the approximation to truth which can thus be obtained.

There is but 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 which are short-lived. Many species, whose structure is complicated, live but for a few years, as the rabbit, while some of the testaceous mollusca, with more simple organization, have a more ex- tended existence. If longevity is not influenced by struc- ture, 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.

The circumstances which regulate the term of existence in different species, exhibit so many peculiarities, corre- sponding to each, that it is difficult to offer any general ob- servations on the subject. Health 1s precarious, and the origin of diseases generally involved in obscurity. The condition of the organs of respiration and digestion, how- ever, 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 m the pro- cesses of combustion, putrefaction, vegetation and respi- ration, there is occasionally a deficiency in particular pla- ces for the supply of animal life. But, im general, where there is a deficiency of oxygen, there is also a quantity of carbonic acid or carburetted hydrogen present. These gases not only mjure the system by occupying the place of

AS

4 PHILOSOPHY OF ZOOLOGY.

the oxygen which is required, but exercise on many spe- cies a deleterious influence. ‘To these circumstances may be referred the difficulty of preserving many fishes and aquatic mollusca 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 cryptogamia, and the respiration of the infusory animalcula. In all cases, when the air of the atmosphere, or that which the water contains, is impregnated with noxi- ous particles, many individuals of a particular species, living im the same district, suffer at the same time. The disease which is thus at first endemic or local, may, by being con- ‘tagious, extend its ravages to other districts.

The endemical and epidemical diseases which attack horses, sheep and cows, obtain in this country the name of murraim, sometimes also the distemper. ‘The general term, however, for the pestilential diseases with which these and other animals are infected is Epizooty, (from sa upon, and Zsey an animal.

The ravages which have been committed among the domesticated animals, at various times, in Europe, by epizooties, 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 happen- ed, that the circumstances which have produced the dis- ease in one species have likewise exercised a similar in- fluence over others.

That these diseases arise from the deranged functions of the respiratory organs, is rendered probable by the cireum- stance, 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.

Many diseases, which greatly contribute to shorten life,

DURATION OF ANIMALS. 5

take their rise from circumstances connected with the or- gans of digestion. Noxious food is frequently consumed by mistake, particularly by domesticated animals. When cows, which have been confined to the house, durmg the winter season, and fed with straw, are turned out to the pastures in the spring, they eat indiscriminately every green plant presented to them, and frequently fall victims to their im- prudence. It is otherwise with animals in a wild state, whose instincts guard them from the common noxious sub- stances 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 defi- ciency,—feebleness is speedily exhibited,—the cutaneous and intestinal animals rapidly multiply, and, in conjunc- tion, accelerate the downfal of the system.

The power of fasting, or of surviving without food, pos- sessed by some animals, is astonishingly great. An eagle has been known to live without food five weeks,—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 be- long 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 sin. gular resources which may be employed in cases where, without it, life would speedily be extinguished.

In situations where animals are deprived of their aceus- tomed food, they frequently avoid the effects of starvation, by devouring substances to which their digestive organs are

6 PHILOSOPHY OF ZOOLOGY.

not adapted. Pigeons can be brought to feed on flesh, and hawks on bread. Sheep, when covered with snow, have been known to eat the wool off each other’s backs. 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 ex- cite vomiting; and probably to cleanse their intestines from obstructions, cr worms, by its mechanical effects. Many land animals promote their health by bathmg, others by rolling themselves in the dust. By the last operation, they probably get rid of the parasitical insects with which they are infected.

But independent 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 a- gainst species, and neutrality is nowhere respected. ‘Those which are preyed upon, have certain means which they em- ploy to avoid the foe; but the rapacious are likewise qua- lified for the pursuit. The exercise of the feelings of be- nevolence may induce us to confine our attention to the for- mer, and adore that goodness which gives shelter to the de- fenceless, and protection to the weak, while we may be dis- posed to turn, precipitately, from viewing the latter; lest we discover marks of cruelty, where we wished to contem- plate nothing but kindness. These feelings are usually the companions of circumscribed and partial observation, and fall far short of the object at which they aim.

It would be impious in us to inquire why the waster has been created to destroy. It is enough if we know that ra- pacious animals occupy a station in the scale of being. And,

DURATION OF ANIMALS. 7

while we eagerly explore the various methods employed by the defenceless, to secure themselves from danger, and evade the threatened death ; it is suitable for us likewise to contem- plate the various means employed by carnivorous animals to gain the means of their subsistence. When we see a hawk in pursuit of a lark, we are apt to admire exclusively, the dex- terity of the latter in avoiding destruction, and to triumph ‘when it has obtained the requisite protection in a thicket. We seem to forget that the digestive organs of the hawk are fitted only for carrion; and we lose sight of the benevo- lence and wisdom exhibited, in giving to its wings a power of inflicting a deadly blow, and rendering the claws suited for grasping, and the bill for tearing in pieces the quarry. We are not therefore to take confined views of the animal kingdom, if we wish to read the lessons concerning the Pro- vidence of God which it teaches. He that causeth the grass to grow for the cattle, and herb for the service of man ; likewise giveth meat in due season to the young lions which roar after their prey ; and feedeth the ravens, though they neither sow nor reap. We sce rapacious and defenceless animals existing, yet we do not observe the former success- ful im extirpating the latter. Limits are assigned to the ravages of this universal war. ‘The excess only of the po- pulation is cut off,—and this excess, on whose production so many animals depend for subsistence, is as uniform as the means used to restrain its limits.

These various circumstances which we have now enume- rated as limiting the duration of animals, preserve the ba- lance of life, restrai within suitable bounds the numbers of the mdividuals of a species, and give stability to that system, the wise arrangements of which can only be dis- covered by a close examination of the whole.

8 PHILOSOPHY OF ZOOLOGY.

CHAP. II.

ON THE DISTRIBUTION OF ANIMALS.

TS examining the zoological productions of different coun- tries, we observe, that the species which are commonly met with in one district, are rare, or not to be detected, in the others. If we confine our attention to any one species, we shall observe, that there is some particular country where the individuals are most numerous, and where the energies of life are exerted with the greatest activity. As we recede from this district, the individuals become less numerous, their increase goes on at a slower rate, and those which are produced are rated of dwarfish stature: at length, we reach the limits beyond which they do not extend. ‘The geogra- phical distribution of each species, therefore, may be re- presented by a circle, towards the centre of which, existence can be comfortably maintained ; but as we approach the cir- cumference, restraints multiply, and life at last becomes im- practicable. Each species has a range peculiar to itself, so that the circles of different species inter sect one another in every possible relation.

The extent of the earth’s surface over which the indivi- duals of a species are dispersed, can only be ascertained af- ter a long series of observations, conducted by naturalists in different countries. Hitherto the geographical limits of but few species have been satisfactorily determined. These chiefly belong to the larger species of quadrupeds, as the African and Asiatic elephants, the ass and the quagga, the lion, hippopotamus, and polar bear. In the tribes of the less perfect animals, the species of which have been investi- gated by few, the extent of their Grocraruicat Disrri- BUTION has been very imperfectly determined. |

TEMPERATURE. Gg

Before proceeding to the examination of the laws which regulate the geographical distribution of any one species, it is expedient that we previously make ourselves acquait- ed with the range of country it inhabits, the situations in which it has been observed, and the peculiar characters it exhibits in these different situations. But while this mi- nute and varied information is requisite for the purpose of investigating fully the physical history of any one species, it is enough, for ordinary investigations, that we ascertain those districts and situations where the individuals are most healthy and most prolific, and those where they do not ex- ist. By comparing the physical circumstances of the for- mer with those of the latter, it will be no difficult matter to discover those conditions which promote the vigour of life in the one, and restrain or destroy its energies in the other. What, then, are those conditions which limit the geographical distribution of species? ‘They appear to be limited to circumstances connected with 'l'emperature, Food, Situation, and Foes.

I. TEMPERATURE.

We have already stated, that the degree of heat at the equatorial regions appears to be most favourable for the in- crease of living beings, and that they diminish in numbers as we approach the poles. There is no latitude, however, which the perseverance of man has yet reached, where living be- ings have not been observed. The icy shores of the arctic regions are peopled as well as the arid plains or shaded fo- rests of tropical climates. When, however, an inhabitant of the colder regions is transported to a warmer district, ihe mereased temperature is painful, the functions be- come deranged, and disease and death ensue. The inhabi- tants of the warmer regions, when transported to the colder districts, experience inconvenience from the change of tem-

10 PHILOSOPHY OF ZOOLOGY.

perature, equally hurtful to the system, and fatal to its continuance. The polar bear appears to be accommodated to live in a region, whose mean annual temperature is be- low the freezing pomt. In the summer temperature of Edinburgh, however well supplied with food, he appears to languish im misery. Cold spring-water poured upon him seems to revive him for a little; but all relief is temporary, the climate is too hot for the enjoyment of life. Destined to live in a climate where the system is required to secrete heat chiefly, it seems incapable of generating the cold re- quisite to counteract the effects of even a temperate climate. The iwhabitants of the torrid regions, on the other hand, seem capable of generating cold chiefly, all their organs being adapted for resisting high temperatures ; and hence, when brought to cold districts, they are incapable of gene- rating the requisite degree of heat.

In those districts where the individuals of a species are most vigorous and prolific, the temperature most suitable for existence prevails. The native country of the horse is probably Arabia. There he exists in a wild state in the greatest numbers. In the Zetland Islands, where he is nearly in a state of nature, he is approaching the polar li- mits of his distribution. He has become a dwarf. He does not reach maturity until his fourth year, seldom con- unues in vigour beyond his twelfth, and the female is never pregnant above once in two years. At the line where the energies of the horse terminate, however, the rein-deer be- comes a useful substitute. Its equatorial limits do not reach the shores of the Baltic.

The variations of the seasons, which bring along with them correspondmg changes of heat and cold, exercise a powerful influence on the distribution of animals, in refe- rence to temperature. Some species appear to possess a considerable range of temperature, within which life can be

TEMPERATURE. li

easily preserved, and all its functions regularly performed. We do not mean to intimate, that there is any animal which can live in our climate, for example, and remain uninfluen- ced by a difference of temperature of upwards of twenty degrees between summer and winter. ‘The constitutional arrangement suited to the one season, would be prejudicial during the continuance of the other. But there are many animals which live in the same district both in summer and winter, and even in districts differmg considerably in their mean annual temperature. What, then, are the means employed by these species to preserve life in the midst of such vicissitudes? The power of producing heat or cold, is a property obviously possessed by the warm-blooded ani- mals, and probably in an inferior degree by those which are termed cold-blooded. But in all the efforts made by the system to secrete extraordinary degrees of either heat or cold, there is so great a portion of vital energy expended, that exhaustion and death follow its long continuance. In all cases where the influence of the seasons are to be resisted by efforts of this kind, it would be requisite to continue them uninterrupted for many months. ‘These efforts, however, are diminished in extent and duration by a variety of the most wonderful arrangements, exhibiting the infinite re- sources of that Wisdom which planned the constitution and continuance of the animal kingdom. To the chief of these compensating or counteracting circumstances we shall now

briefly advert.

1. Changes take place in the Quantity of the Clothing. The same circumstances which enable the Negro to go about in a state approaching to nakedness, and impel the inhabi- tants of the arctic regions to cover themselves with woollen cloth or skins, operate in regulating the clothing of quad- rupeds and birds. In the warmer regions, it is requisite to suffer the temperature of the Body to be diminished, while,

12 PHILOSOPHY OF ZOOLOGY.

in the colder regions, the very opposite object is aimed at.

In the former case, the hair or feathers are thinly spread over the body, while, in the latter, they form a close and continuous covering. In the dogs of Guinea, and in the African and Indian sheep, the fur is so very thin that they may almost be denominated naked. In the Siberian dog and Iceland sheep, on the other hand, the body is protected by a thicker and longer covering.

The clothing of animals, living in cold countries, is net only different from that of the animals of warm regions in its quantity, but m its arrangement. If we examme the covering of swine of warm countries, we find it consisting of bristles or hair of the same form and texture; while the same animals which live in colder districts, possess not only common bristles or strong hair, but a fine frizzled wool next the skin, over which the long hairs project. Between the swine of the south of England, and the Scottish High- lands, such differences may be observed. Similar appear- ances present themselves among the sheep of warm and cold countries. ‘The fleece of those of England consists entirely of wool; while the sheep of Zetland and Iceland possess a fleece, containing, besides the wool, a number of long hairs, which give to it, when on the back of the animal, the ap- pearance of being very coarse. The living races of Rhin- oceros and Elephant, inhabitants of the warm regions, have scarcely any hair upon their bodies; while those which formerly lived in the northern plains of Europe, the entire carcases of which have been preserved in the ice in Si- beria, were covered with fur similar to the Icelandic Sheep, consisting of a thick covering of short frizzled wool, protect-

_ ed by long coarse hairs. These species, now extinct, pos- sessed clothing suiting them for the climate where they lived, and where they became at last enveloped in ice. Had they been transported by any accident from a warmer

CLOTHING OF ANIMALS. 13

region, they would have exhibited in the thinness of theit covering, unequivocal marks of the climate in which they were reared. *

By means of this arrangement, in reference to the quan- tity of clothing, individuals of the same species can main- tain life, comfortably, in climates which differ considerably in their average annual temperature. By the same arrange- ments, the individuals residing in a particular district, are able to provide against the varying temperature of the sea- sons. The covering is diminished durmg summer and in- creased in winter, as may be witnessed in many of our do- mestic quadrupeds.

Previous to winter, the hair is increased in quantity and length. This increase bears a constant ratio to the tempe- rature; so that when the temperature decreases with the elevation, we find the cattle and horses, living on farms near the level of the sea, covered with a shorter and thin- ner fur than those which inhabit districts of a higher level. Cattle and horses, housed during the winter, have shorter and thinner hair than those which live constantly in the open air. The hair is likewise shorter and thinner in a mild, than during a severe winter.

This winter covering, if continued during the summer, would prove inconveniently warm. It is, therefore, thrown off by degrees as the summer advances ; so that the animals which were shaggy during the cold months become sleek in the hot season.

This process of casting the hair takes place at different seasons, according to the constitution of the animal with respect to heat. ‘The mole has, in general, finished this operation before the end of May. The fleece of the sheep, when suffered to fall, is seldom cast. before the end of June. In the northern islands of Scotland, where the shears are never used, the inhabitants watch the time when the fleece

T4 PHILOSOPHY OF ZOOLOGY:

is ready to fall, and pull it off with their fingers. The long hairs, which likewise form a part of the covermg, remain for several weeks, as they are not ripe for casting at the same time with the fine wool. This operation of pullmg off the wool, provincially called roving, is represented by some writers, more humane than well-informed, as a pain- ful process to the animal. That it is not even disagreeable, is evident from the quiet manner in which the sheep he during the pulling, and from the ease with which the fleece separates from the skm.

We are in general inattentive with respect to the annual changes in the clothing of our domestic animals; but when in search of those beasts which yield us our most valuable

furs, we are compelled to watch these operations of the seasons. During the summer months the fur is thin and short, and is scarcely ever an object of pursuit ; while dur- ing the winter, it possesses in perfection all its valuable qualities. When the beginning of winter is remarkable for its mildness, the fur is longer in *%pening, as the animal stands in no need of the additional quantity for a covering ; but as soon as the rigours of the season commence, the fleece speedily increases in the quantity and length of hair. This increase is sometimes very rapid in the hare and the rabbit, the skins of which are seldom ripe in the fur un- til there is a fall of snow, or a few days of frosty weather ; the growth of hair in such instances being dependent on the temperature of the atmosphere.

The moulting of birds is another preparation for winter, which is analogous to the casting of the hair in quadru- peds. During summer, the feathers of birds are exposed to many accidents. Not a few spontaneously fall ; some of them are torn off during their amorous quarrels ; others are broken or damaged; while in many species they are

pulled from their bodies to hne their nests. Hence their

CLOTHING OF ANIMALS. 15

summer dress become thin and suitable. Previous to win- ter, however, and immediately after the process of incuba- tion and rearing of the young is finished, the old feathers are pushed off in succession by the new ones, and in this manner the greater part of the plumage of the bird is re- newed. During this process of moulting, the bird seems much enfeebled, and, if previously in a weak state, is m danger of dying during the process. In consequence of this renewal of the feathers, the winter covering is render- ed perfect, and the birds prepared for withstanding all the rigours of the season. In those birds whose plumage changes colour with the seasons, the moulting takes place in sub- serviency to the purposes of these variations, as we shall shortly have occasion to notice.

By this addition to the non-conducting appendices of the skin, quadrupeds and birds are enabled to preserve the heat generated in their bodies, from being readily transmitted to the surrounding air, and carried off by its motions and diminished temperature. But along with a change of quantity, there is frequently also a change of colour.

2. Changes take place in the Colour of the Clothing.— The distribution of colour m the animal kingdom, appears to be connected with latitude ‘us correlative with tempera- ture. In the warmer districts of the earth, the colours of man, quadrupeds and birds, exhibit greater variety, and are deeper and brighter, than in the natives of colder coun- tries. y

Among the inhabitants of the temperate and cold re- gions there are many species which, in reference to the co- lour of their dress, do not appear to be influenced by the vicissitudes of the seasons. In others, a very marked dif- ference prevails between the colour of their summer and

16 THILOGSOPHY OF ZOOLOGY.

winter garb. A few of the more obvious instances 6f these changes, in British species, may be here produced.

Among quadrupeds, the Alpme hare (Lepus variabilis) is a very remarkable example. It is found, in this country, on the high mountains of the Grampian range. Its sum- mer dress is of a tawny grey colour ; but, about the month of September, its fur gradually changes to a snowy white- ness. It continues in this state during the winter; and re- sumes its plainer covering again m the month of April or May, according to the season. The ermine is another of our native quadrupeds which exhibits in its dress similar changes of colour according to the season. It frequents the outskirts of woods and thickets. Durmg the summer months, its hair is of a pale reddish brown colour ; in har- vest it becomes clouded with pale yellow; and, in the month of November, with us, it is of a snow white colour. Its winter dress furnishes the valuable fur called ermine. Early in spring, the white becomes freckled with brown, and in the month of May it completely resumes its summer garb. .

Among the feathered tribes such instances of change of colour in the plumage during winter are numerous. ‘They greatly perplex the ornithologist, and have been the means of introducing into the system several spurious species. The white grous or ptarmigan (T'etrao lagopus) may be produced as a familiar example of this kind of hybernation. This bird, like the Alpme hare, inhabits the higher Gram- plans, and is never found at a great distance from the limits of the snow. In summer its plumage is of an ash colour, mottled with small dusky spots and bars. At the approach of winter the dark colours disappear, and its feathers are then found to be pure white. In remarkably mild winters the change is sometimes incomplete, a few dusky spots of the summer dress remaining. In spring its winter garb

CLOTHING OF ANIMALS. ny becomes again mottled, and the bird loses much of its beauty. Even the young bird: in their autumnal dress re- semble their parents in the mottled plumage, which hke- wise becomes white at the approach of winter.

Among the aquatic birds, similar changes m the colour of the plumage have been observed. The black guillemot ( Uria grylle), so common on our coasts, is of a sooty black colour during the summer, with a white patch on the wings. During winter, however, the black colour disappears, and its plumage is then clouded with ash-coloured spots on a white ground. In the winter dress it has been described by some as a distinct species, under the name of the spotted guillemot. In the more northern regions, as in Greenland, for example, this bird, in winter, becomes of a pure white colour.

These changes of colour, which we have already men- tioned, extend throughout the whole plumage of the bird ; but, in some instances, the change takes place on a small part only of the plumage. Thus the little auk (Alca alle), during summer, has its cheeks and throat of a black colour, but in winter these parts become of a dirty white. In this its winter garb, it is often shot on our coasts. Its sum- mer dress induced PEewnnanr to consider it as a variety, and as such to give a figure of it in his British Zoology. The black-headed gull (Larus ridibundus) has a black head during summer, as its English name intimates. Du- ring the winter, however, the black colour on the head disappears; and, when in this dress, it has been regarded by many as a distinct species, under the name of the Red- legged Gull.

In many other birds there is a remarkable difference, in point of colour, between the summer and the winter plu- mage, although not so striking as in those which we have already noticed. The colours of the summer feathers are

VOL. Il. B

is PHILOSOPHY OF ZOOLOGY.

rich and vivid; those of the winter obscure and dull. This is well illustrated in the dunlin (T7'ringa alpina), whose summer plumage is much imtermixed with black and ru- fous colour, but whose winter plumage is dull and cine- reous. In its winter dress it has been described as a dis- tinct species, under the name of 7’. cinclus, or Purre. Si+ milar instances might be produced in the wagtails, lin- nets, and plovers, and a great many other birds.

The circumstances under which these changes are ob- served to take place, indicate their dependence on tempera- ture, as connected with the season. The deep colours of the summer dress are exchanged for the lighter or whiter colours of the winter, with a rapidity and extent propor- tional to the changes of the seasons. During a mild autumn, the shifting of the dark for the light coloured dress proceeds at a very slow pace; and when the winter also continues mild, the white dress is never fully assumed. In some species, as the black guillemot, the white winter dress is never acquired in this climate, although its ash-coloured plumage intimates a tendency to the change. In the cli- mate of Greenland, on the other hand, the change is com- plete, and the plumage is of a snowy whiteness; as we had an opportunity of observing in the collection of the Dublia Society in 1816, in a specimen in its winter dress, brought from Greenland by an intelligent and enterprising natural- ist, Sir Cuartes G1EsEcKE’.

Having thus seen that the colour of the clothing of many animals changes with the season, and that, however diver- sified the summer dress may be, the colour during winter _ approaches to white, it may now be asked, What benefit is derived from this arrangement * ?

* Some species of gulls exhibit in their winter plumage very striking de-. viations from this general rule. Monracv, in his Supplement to the Orni-

CLOTHING OF ANIMALS. 19

The rate at which bodies cool is greatly influenced by their colour. The surface which reflects heat most readily, suffers it to escape but slowly by radiation. Reflection takes place most readily in objects of a white colour, and from such, consequently, heat will radiate with difficulty. If we suppose two animals, the one of a black colour, and the other white, placed in a higher temperature than that of their own body, the heat will enter the one that is black with the greatest rapidity, and elevate its temperature con- siderably above the other. These differences are observ- able in wearing black and light coloured clothes during a hot day. When, on the other hand, these animals are placed in a situation, the temperature of which is consider-

thological Dictionary, article Common Gull, says,—‘‘ We have had this species alive for some years, and observed, that when it had attained its full mature plumage, in the second year, the head and neck is pure white during the summer; but, like the herring gull, these parts become streaked, and spotted with brown, in autumn, which is continued all the winter; and in the spring become again pure white.” When speaking of the herring gull, he says,—‘ This gull is now living, and in high health, being thirteen years old. It begins moulting about the middle of August, when it annually as- sumes the mottled head and neck ; and about the middle of February, the partial spring moulting commences, the mottled feathers are discharged, and succeeded by pure white.” A herring gull, at present six years old, in the garden at Canonmills, of my esteemed friend Mr P. Netti, has, for the last three years, regularly acquired the mottled plumage of the head and neck, in the month of August. It did not acquire the pure white head and neck in spring and summer, before the third year. Captain Sazine, in his valuable Memoir on the Birds of Greenland, Linn. Trans. vol, xii. p. 544, when de- scribing the changes of plumage which the Larus glaucus exhibits, adds,— “¢ In winter, the mature bird has the head and neck mottled with brown, as is usual with all the white-headed gulls.” Ina specimen of L. marinus, shot in winter, I observed on the head, and chiefly in front of the eyes, a few black hairs, which were formed from the produced ends of the shafts. BQ

2g PHILOSOPHY OF ZOOLOGY.

ably lower than their own, the black animal will give out its heat by radiation to every surrounding object colder than itself, and speedily have its temperature reduced ; while the white animal will part with its heat by radiation at a much slower rate. The change of colour in the dress of animals is therefore suited to regulate their temperature by the radiation or absorption of caloric.

While it is requisite that the temperature of some species should be preserved as equably as possible, the cooling ef- fects of winter are likewise resisted by an additional quan- tity of heat being generated by the system. An increase in the quantity of clothing takes place to. prevent that heat bemg dissipated by communication with the cold ob- jects around, and the dress changes to a white colour, to prevent its loss by radiation. In summer, the pernicious increase of temperature is prevented by a diminished secre- tion of heat or the secretion of cold, creased perspiration, the casting of a portion of the winter covering, and by a superior intensity of colour in the remainder giving it a greater radiating power. ‘This last character would, in the sunshine, by absorbing heat, prove a source of great in- convenience, were its effects not counterbalanced by other arrangements, and by the opportunity of frequenting the refreshing shade, or bathing in the stream.

In those cases, where particular parts only of the cloth- ing change their colour, there are probably local cireum- stances connected with the secretions, or the sexual system, which render such arrangements necessary. Hair growing from a part which has been wounded, is always paler colour- ed. than that which is produced on the sounder parts, inti- mating the operation of local causes on the colouring secre- tions, or local purposes to be served by the change.

It is probably for the purpose of preventing a wasteful dissipation of the heat of the system, that the dress of many

CLOTHING OF ANIMALS. pH |

‘ammals becomes lighter coloured in old age, and that the human hair turns grey. Young animals seldom present the same dress and vivid colours, &c. which they assume upon arriving at maturity *.

The change of colour which takes ‘piace in the dress of some animals during winter, is supposed to serve other purposes than the regulation of their temperature. ‘The white garb which they assume, assimilates them ‘to the colour of the snew, and in this way they are considered as better able to escape the observation of their foes.

All our conclusions concerning final causes, ought to be the result-of very extended observations, lest we delineate arrangements which would be productive of pain and ruin to many species, where we intended to unfold the marks of wisdom and benevolence. If the white dress of the al- pine hare and ptarmigan concealed them from their ene- mies, the eagle, the cat, and the fox, these last, by being deprived of their ordinary food, would be in danger of starvation and death. But this variation of colour is not confined to weak or defenceless animals. Beasts and birds of prey are likewise subject -to the change. Hence, if it yielded protection to some, it would enable others to prey with greater certainty of success on their defenceless neighbours. Many of these rapacious animals, (as the er- mine for example, which is at all times well qualified to provide for its wants by its determined boldness, extreme agility, and exquisite smell), do not stand in need of such assistance. If this change extends’to the rapacious as well

* Young guils and solan geese, however, present very obvious excep- tions. Their darkest colours are those of immaturity. Yellow seems a pre- dominant tint of infancy. The hoofs of quadrupeds, and the beaks of birds, are usually more or less tinged with this colour at birth.

99, PHILOSOPHY OF ZOOLOGY.

as the defenceless, it may likewise be cbserved in aqua- tic as well as in terrestrial animals. In reference to acqua- tic animals, we would ask, What protection is afforded to the black guillemot, during the winter, by its mottled plu- mage, or to the little auk, by its white chin, since the whiter their dress, so much the more unlike the dark coloured water of the clouded season in which it is exhibited? The popular opinion on the subject must be relinquished as un- tenable ; especially as the change of colour from dark to white does not vary, however different the habits or even stations of the animals may be in which it takes place.

An interesting inquiry yet remains to be made regard- ing the manner in which this change in the colour of the dress is effected. 'The attention of naturalists has, of late years, been directed to this subject, and several important observations have been made, equally interesting to the phy-= siological and systematical zoologist.

From the belief which is generally entertained, that in hair and feathers there is no circulation, neither secre- tion nor absorption, a conviction arose in the minds of many naturalists, that the change of colour which takes place in the dress of some animals according to the season, was not the effect of any organical change in the hair or feathers, but accompanied a renewal of the whole. The late Grorcr Montacu, Esquire, who had long attended to the characters and habits of the feathered tribes, delivers his opinion on this subject in the following terms: Some species of birds seem to change their winter and summer feathers, or at least in part ; in some, this is performed by moulting twice a-year, as in the ptarmigan, in others, only additional feathers are thrown out. But we have no con- ception of the feathers changing colour, although we have deen informed of such happening in the course of one

CLOTHING OF ANIMALS. ‘OS

night *.” Staggered with the statements of such a frequent renewal of the dress of animals, accompanied by such a wasteful expenditure of vital energy, and guided by multi- plied observations, we ventured to offer the following re- marks on the subject in the Edinburgh Encyclopedia, un- der the article Hybernation,” vol. xi. p. $87, published in 1817. ,

Tt has been supposed by some, that those quadrupeds which, like the alpine hare and ermine, become white in winter, cast their hair twice in the course of the year ; at harvest when they part with their summer dress, and in spring when they throw off their winter fur. This opinion does not