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74 
FIRST CLASS OF THE VERTEBRATED ANIMALS. 
move in obscurity through fear of their enemies. Thus, the Hats, Dormice, and 
Hares, come from their retreats in the evening, or very e.Trly in the morning. 
The Edentata, such as the Armadillos, Anteaters, and Maiiis, are also nocturnal, 
through timidity and their want of offensive arms. 
The Pachydermata and Ruminantia, on the contrary, feed only during the day. 
With all these aiiimals, the remaining part of the twenty-four hours is devoted to sleep 
and repose. Crepuscular feeders sleep partly during the night and partly during the 
day, while diurnal sleepers arc nocturnal feeders, but in all cases the same round of 
functions succeeds in equal periods of twenty-four hours. 
Tlic time selected by each animal for its period of food or repose is capable of 
undergoing much modification, from the presence or absence of particular stimuli, 
such as the different states of the air, the states of electricity, moisture, and heat, at 
the several periods of the day and night. The presence or absence of Light and Heat 
seems chiefly to regulate the periods of activity and repose in all animals. Tiie Day 
being warmer than the Night, tends to establish in some of the bodies a movement 
towards the surface,— a period of waste and destruction of force, — the Night with 
these is devoted to a reparation and accumulation of energy. 
The dependance of certain functions of animals upon the presence or absence of 
Light, becomes more perfect when any particular formation of their visual organs 
specially marks them out for enduring Light of difl’erent degrees of intensity. When 
animals run into white varieties, as may often be observed in white Negrons, Albinos, 
white Rabbits, Mice, Dogs, Cats, Pigeons, and many others, their eyes are commonly 
red ; and these organs then become so acutely sensible to light, that they are unable 
to support the full blaze of day ; but at the same time, they can sec much more 
clearly in twdigbt than individuals which have not experienced this degeneration. 
The cause of this extreme sensibility in their visual organs is completely ascer- 
tained. If we examine the inside of the Sclerotica and Iris, which commonly form 
the obscure chamber of the eye, we shall find in the leucoso individuals, that these 
membranes are deprived of the black or brown pigment which is designed to defend the 
eve from the rays of Light, except at the transparent aperture of the pupil. The 
retina being thus insufficiently defended against the luminous rays, becomes easily 
dazzled in bright daylight, but receives a sufficient number of rays in the twilight for 
the animals to see clearly. An opposite clTect is produced in black or brown indivi- 
duals, such as the Negroes, in whom this pigment {pi^mentmn nigrum) which lines 
the interior of the sclerotica and iris, defends it perfectly from the entrance of lumi- 
nous rays, excepting at the proper aperture of the pupil. For this reason, Negroes, 
and generally all individuals witli black eyes, can easily support the full blaze of sun- 
shine, while the blue, gray, or ash-coloured eyes of the fairer inhabitants of Europe 
are so tender, from the intensity of the tropica! sun, that they require to be defended 
by coloured glasses, else they become affected with ophthalmia. 
IMcn and the lower animals, with very white skins and light hair, are thus destitute 
of that brown or black colouring matter, which not only lines the sclerotica and iris, 
but also impregnates the mucous tissue under the skin, and, passing onwards, tinges 
the hair or fleece of different colours. Black or chestnut hair usually accompanies an 
iris more or less brown. It thus follows, that black and dark-brown animals can 
endure the blaze of day, and that the light-brown or white animals, which are natu- 
rally better adapted for the cold and polar regions of the earth, become the most 
proper to see during the twilight or at night. All the nocturnal animals are 
further capable of dilating their pupils largely in the dark, in order to receive a larger 
pencil of rays tlian the diurnal animals; the latter, on the contrary, arc compelled to 
close the pupil to avoid being dazzled. The inhabitants of the polar regions possess 
this power of dilating and contracting the pupil in a remarkable degree, as they ex- 
perience, at one season of the year, the dazzling reflections of the snow, and at an- 
other, the long twilights and .Aurorjc Boreales of winter. 
When deprived more or less of this pigment, Man .md the lower animals have a 
very sensitive skin, the fibres of which ai-e delicate and slim, while their hair is light, 
fine, and silky. These individuals are easily overcome by the heat of the day and the 
intensity of its light ; they soon become exhausted during the day, and find the feeble 
rays of the night better proportioned to the delicacy of their temperament. Hence, 
hey transform the Day into a period of repose, the Night into one of activity and 
exertion. 
AVehave a further confirmation of the accuracy of these cb.^ervations in the fact, 
that with the greater part of the nocturnal animals, the colouring pigment of the skin 
is less vivid than in the diurnal races. It may generally be remarked, that animals 
with nocturnal eyes are clad in a raomnfiil and dingy vestment of gray or as-h-colour, 
striped with black or spotted, not only among the HJamraalla and Birds of Night, but 
even in the Insects, when we compare them to the allied diurnal species* We see a 
remarkable contrast between the tints of the diurnal Butterflies and those of the 
Moths and Sphinges. The Owls are sad luid sombre birds when placed against the 
Parroquets or Humming Birds, glittering in the brilliant sun of the torrid zone. 
Many atnniaU of the Cat kind, the Lemurs and Bats, cannot compare in these respects 
with the gayer quadrupeds. 
Nocturnal animals further possess the peculiar quality of advancing to surprise 
their jirey w ith a noiseless step. The almost imperceptible flight of Nocturnal Birds 
of prey is well kiionn to proceed from the soft feathers of their wings ; and the same 
eflect is produced by the wings of the Bats, and the nocturnal Butterflies. The cre- 
puscular Sphinges alone produce a humming noise by the vibration of their wings ; 
but they suck the nectar of fiow'crs, and the Bombyx and Cossiis do not take animal 
food. AU other nocturnal animals are, fur the most part, carnivorous, attack their 
prey by surprise — and Nature inspii'es tliera with the same instinct as the cow’ai’div 
assassin, who dues not dare to face his enemy in the blaze of day. In return, how- 
ever, they are often impregnated with fetid odours, which serve to announce their 
approach. 
It is thus to the peculiar constitution of their bodies that the nocturnal animals 
owe their property of sleeping during the day and waking at night, a peculiarity so 
opposite to other being?. An analogous state exists also in the Vegetable kingdom. 
Some flowers appear to close and languish during the heat of the day. The 
sun acts too vividly upon the frail texture of certain petals, and occasions the sap and 
nutritious fluids which fill their laminm to evaporate too freely; but during the fresh- 
ness of night the sap aud juices being less dissipated, accumulate in the tissues of 
these plants, their canals are dilated, and the flowers and leaves expand. Their ten- 
der organs of reproduction would soon become dossicated by the heat of the sun : 
hence the plant withdraws them from its influence, and displays them only before tluj 
pale light of the moon. Diurnal flowers also have, with animals, a more solid tissue 
than the nocturnal. The former require to be stimulated by light aud heat, that their 
reproductive organs may develop themselves, while the more tender nocturnal floweis 
resemble those animals of the night which shield their eyes from the dazzling influence 
of the day-light. Further, the sexual organs of Nocturnal Plants fade more ra- 
pidly than the diurnal: their monopctalous and polypetalous corollae are of a texture 
extremely frail, generally blanched and etiolated. Their evanescent perfume is exhaled 
only at night ; it fails during the day. 
In general, all nocturnal beings, whether Mammalia, Birds, Reptiles, Fishes, Ir>- 
sects, or Plants, present sombre and tarnished hues, while the diurnal species, under 
the fiery influence of the sun, assume garments of dazzling brilliancy. Light thus 
stimulates to activity, and is or4e of the principal causes of the development in organ- 
ized beings of animal and vegetable poisons and perfumes, when acting upon special 
constitutions. Darkness benefits those acrid, venomous, faded, and inert plants, whose 
juices, feebly elaborated, require its shelter : it is favorable to the development of 
animals generally at their birth — to the lai vm of insects in their dark asylum.s to 
mushrooms aud lichens, the mysterious product of evanescent sporulcs, in the deptlis 
of forests, and the hollows of caverns — and in general to all feeble and imperfect or- 
ganizations. The moisture and coldness of night are further unfavorable to the 
waste of living bodies, and hence it is the period when they experience the highest 
degree of growth and vegetation, provided that the cold be not too intense. In fact, 
the internal functions of nutririon and repair are performed more intensely during the 
repose of night, and the absence of external stimuli. Then the organs grow, and be- 
come replenished with nutritious fluids. Thus the mushrooms ai e mostly the offspring 
of the night, or multiply in the secret obscurity of subterranean excavations. 
Each day, like each season, distributes to every living being some portion of heat, 
light, and nutriment, and measures the rhythm of their functions of waking or sleep- 
ing, nutrition or excretion. When these are maintained in harmony with the 
movements of the globe, health and regularity are alike maintained. We find the 
influence of the periodic return of day and night in places where its presence could 
scarcely have been anticipated. According to the researches of Messieurs Burch, 
Quetolet, and Villermc, the mortality of the human species increases towards sun- 
rise, diminishes towards sun-set, and almost no deaths happen at nud-day. Further, 
it is observetl that births occur most frequently during the night, and deaths during 
the day. Births and deaths are generally most numerous between thehours of three aud 
six in the morning, aud least numerous from three to six in the evening, corresponding 
to the maximum and minimum of temperature. Tliis prevails as welkin the seasons 
the year- as in the hours of the day. Tlie greater number of births and deaths occur in 
the most stimulating periods of the day and year, being ilt six in the morning, and 
in the month of April. Those periods, on the contrary, when stimuli begin to fail, 
are most deficient in births and deaths, such as three o’clock in tlm afternoon, and iu 
the month of August. The paroxysms of fevers, aud the pains of an approaching 
accouchcmeiU, usually begin in the evening, while the crisis or result arrives towards 
the morning. 
Thus there exists a remarkable correspondence between the structure of animals 
and plants, and that periodical order of light aud darkness rcsul ,ing from the rotation 
of the earth around its axis. Although this succession of functions depends partially 
on the presence of the external stimuli of light and heat, yet there appears to be '* 
diurnal period belonging to the constitution both of animals and vegetables, and this 
structure corresponds with the astronomical day. The power of accommodation pcs-’ 
sessed by living beings iu this respect, is not sufficient to allow us to suppose that the 
periods of the day and night could be very greatly lengthened or shortened without 
causing their ultimate destruction. “ We may be tolerably certain,” says JL' 
Whewell, “ that a constantly recurring period of forty-eight hours would be too long 
for one day of employment, and one period of sleep, with our present faculties ; and 
all whose bodies and minds are tolerably a<;tivo will probably agree that, independently 
of habit, a perpetual alternation of eight hours up, and four in bod, would employ the 
human powers less advantageously and agreeably than an alternation of sixteen and 
eight, A creature which could employ the full energies of his body and mind unin- 
terruptedly for nine months, and then take a single sleep of three mouths would nut 
be a man. When, therefore, we have subtracted from the daUy cycle of the employ' 
mont of men and aiiimals, that which is to be set down to the account of habits ac ' 
quired, and that which is occasioned by extraneous causes, there still remaina a 
periodical character, and a period of a certain length, which coincides with* 
or at any rate easily accommodates iUelf to, the duration of the earth’s revo- 
lution. Wo can very easily conceive the Earth to revolve on her axis faster 
or slower than she does, aud thus the days to be longer or shorter than they 
are, without supposing any other change to take place. There is no apparent 
reason why this globe should turn on its axis just three hundred and sixty-five times 
while it describes its orbit round the sun. The revolutions of the other planets, as A*** 
as wc know them, do not appear to follow any rule by which they are connectcvl with 
the distance from the Sun. Mercury, Venus, and Mars, Imve days nearly the length 
of ours. Jupiter and Saturn revolve in about ten hours each. For any thing we can 
discover, the Earth might have revolved in this or any other smaller period, er "t 
might have had, without mechanical inconvcnieocc, much longer days than we ha'<* 
But the terrestrial day, and consequently the length of the cycle of light and darkno'* 
being what it is, we find various parts of the constitution, both of animals and veget- 
ables, which have a jicriodical character corresponding to tlie diurnal succession ^ 
exleruAl conditions; and wc find the length of the period, as it exists iu their co» 
stitution, coincides w ith the length of the uatur.il day. 
Tho want of colour, or Albinism, in animal and vegetable bodies, when they 
said to be leucosa or white, has its proximate cause iu the original want, or the 
diminished secretion, of the coloured layer of mucous uct-work placed immediately 
