74 



FIRST CLASS OF THE VERTEBRATED ANIMALS. 



move ill obscurity through fear of their enemies. Thus, the Rats, Dormice, and 

 Plares, come from their retreats in the evening, or very early in the morning. 



The Edentata, such as the Armadillos, Anteaters, and Blanis, are also nocturnal, 

 through timidity and their want of offensive ai-ms. 



The Pachyderraata and Ruminantia, on the contrary, feed only during the day. 

 With all these animals, the remaining part of the t-.venty-four hours is devoted to sleep 

 and repose. Crepuscular feeders sleep partly during the night and partly during the 

 day, while diurnal sleepers are nocturnal feeders, but in all cases the same round of 

 functions succeeds in equal periods of twenty-four hours. 



The 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 Pleat 

 seems chiefly to regulate the periods of activity and repose in all animals. The Day 

 being warmer than the Night, tends to establish in some of the bodies a m.ovement 

 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 different degrees of intensity. When 

 animals run into white varieties, as may often be observed in white Negroes, 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 see much more 

 clearly in twilight 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 leucose individuals, that these 

 membranes are deprived of the black or brown pigment which is designed to defend the 

 eye 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 sufEicient number of rays in the twilight for 

 the animals to see clearly. An opposite effect is produced in black or brown indivi- 

 duals, such as the Negroes, in whom this pigment (pigmeiitam 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 with 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 tropical sun, that they require to be defended 

 by coloured glasses, else they become affected with ophthalmia. 



Men 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, tinjjes 

 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 than the diurnal animals ; the latter, on the contrary, are 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-j 

 perience, at one season of the year, the dazzling reflections of the snow, and at an- 

 other, the long twilights and Aurora Boreales of winter. 



When deprived more or less of this pigment, Man and the lower animals have a 

 very sensitive skin, the fibres of which are delicate and slim, while their hair is li^ht, 

 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. 



We have a further confirmation of the accuracy of these observations 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 mournful and dingy vestment of gray or ash-colour, 

 striped with black or spotted, not only among the Mammalia and Birds of Nin-ht, 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 and sombre birds when placed against the 

 Parroquets or Humming Birds, glittering in the brilliant sun of the torrid zone. 

 Many animals 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 prey with a noiseless step. The almost imperceptible flight of Nocturnal Birds 

 of prey is well known to proceed from the soft feathers of their wings ; and the same 

 effect 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 wino-s ; 

 Lnt they suck the nectar of flowers, and the Bombyx and Cossus do not take animal 

 food. All other nocturnal animals are, for the most part, carnivorous, attack their 

 prey by surprise — and Nature inspires them with the same instinct as the cowardly 

 assassin, who does not daic 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 ihe nocturnal animals 

 owe their property of sleeping during the day and waking at night, a peculiarity so 

 opposite to other beings. An analogous state exists also in the Vegetable kingdom. 

 Some flowers appear to close and languish during the heat of the day. The 

 Bun acts too vividly upon the frail texture of certain petals, and occasions the sap and 



nutritious fluids which fill their laminte to evaporate too freely ; but duriu" the fresh- 

 ness of night the sap and juices being less dissipated, accumulate in the tissues of 

 these plants, their canals arc dilated, and the flowers and leaves expand. Their ten- 

 der organs of reproduction would soon become dessicated by the heat of the sun ; 

 hence the plant withdraws them from its influence, and displays them only before tho 

 pale light of the moon. Diurnal flowers also have, with animals, a more solid tissua 

 than the nocturnal. The former require to be stimulated by light and heat, that their 

 reproductive organs may develop themselves, while the more tender nocturnal flowers 

 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 monopetalous and polypetalous corolla; 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, In- 

 sects, or Plants, present sombre and tarnished hues, while the diurnal species, under 

 the fiery influence of the sun, assume garments of dazzhng brilliancy. Lio-ht thus 

 stimulates to activity, and is one of the principal causes of the development in ort^an- 

 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 larvse of insects in their dark asylums to 



mushrooms and lichens, the mysterious product of evanescent sporules, in the depths 

 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 tha 

 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 nutrition and repair are performed more intensely during tha 

 repose of night, and the absence of external stimuli. Then the organs grow, and be- 

 come replenished with nutritious fluids. Thus the mushrooms are mostly the offspring 

 of the night, or multiply in the secret obscurity of subterranean excavations. 



Each day, hke 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 tha 

 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, 

 Quetelet, and Villerme, the mortality of the human species increases towards sun- 

 rise, diminishes towards sun-set, and almost no deaths happen at mid-day. Further, 

 it is observed that births occur most frequently during the night, and deaths durirg 

 the day. Births and deaths are generally most nmnerous between the hours of three and 

 six in the morning, and least numerous from three to six in the evening, corresponding 

 to the maximum and minimum of temperature. This prevails as well in the seasons of 

 the year as in the hours of the day. The greater number of births and deaths occur in 

 the most stimulating periods of the day and year, being at six in the raornino-, and 

 in the month of April. Those periods, on the contrary, when stimuH begin to fail, 

 are most deficient in births and deaths, such as three o'clock in tlie afternoon, and in 

 the month of August. The paroxysms of fevers, and the pains of an approaching 

 accouchemerd, usually begin in the evening, while the crisis or result arrives towardi 

 the morning. 



Thus there exists a remarkable correspondence between the structure of animals 

 and plants, and that periodical order of light and darkness resul -ing from the rotation 

 of the earth around its axis. Although this succession of functions depends partially 

 on the presence of the external stimuU of light and heat, yet there appears to be a 

 diurnal period belonging to the constitution both of animals and vegetables, and this 

 structure corresponds with the astronomical day. The power of accommodation pos- 

 sessed by living beings in this respect, is not suflScient to allow us to suppose that tho 

 periods of the day ar^d night could be very greatly lengthened or shortened without 

 causing their ultimate destruction. " We may be tolerably certain," says Sir 

 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 antive will probably agree that, independently 

 of habit, a perpetual alternation of eight hours up, and four in bed, 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 months, would not 

 be a man. When, therefore, we have subtracted from the daily cycle of the employ- 

 ment of men and animals, that which is to be set down to the account of habits ac- 

 quired, and that which is occasioned by extraneous causes, there still remains a 

 periodical character, and a period of a certain length, which coincides with, 

 or at any rate easily accommodates itself to, the duration of the earth's revo- 

 lution. We can very easily conceive the Earth to revolve on her axis faster 

 or slower than she does, and thus the days to be longer or shorter than thev 

 are, without supposing any other change to take place= There is no appareul 

 reason why this globe should turn on its axis just three hundred and sixty-five tim-'s 

 while it describes its orbit round the sun. The revolutions of tho other planets, as far 

 as we know them, do not appear to follow any rule by which they are connected witu 

 the distance from the Sun. i\5ercury, Venus, and I\Iars, have days nearly the length 

 of ours. Jupiter and Saturn revolve in about ten hours each. For any thing we c;in 

 discover, the Earth might have revolved in this or any other smaller period, or we 

 might have had, without mechanical inconvenience, much longer days than we havi'. 

 But the terrestrial day, and consequently the length of the cycle of light and darknet--, 

 being what it is, we find various parts of the constitution, both of animals and vegel- 

 ables, which have a periodical character corresponding to the diurnal succession t^f 

 external conditions j and we find the length of the period, as it exists in their con- 

 stitution, coincides with the length of the natural day." 



The want of colour, or Albinism, in animal and vegetable bodies, when they arc 

 said to ha hvcoss or ichite, has its proximate cause in the oiiginal want, or the 

 diminished secretion, of the coloui-ed layer of raucous net-work placed immediately 



