CHAP. IX.

 

Varieties in  the Generation of Animals.

 

The nutrition and the reproduction of animals and of vegetables, are thus effect by the same matter.  It is a substance universally prolific, and composed of organic particles, the union of which gives rise to all organized bodies.  Nature always works on the same stock, and this stock is inexhaustible.  But the means she employs to give it value ar various; and these general varieties and affinities merit the attention of philosophers, because from them we are enabled to account for particular exceptions to the common plan of her operations.

 

In general, large animals are less prolific than small ones.  The whale, the elephant, the rhinoceros, the horse, man, &c. produce but one, and very rarely two, at a birth.  But small animals, as rats, herrings, and insects, produce a great number.  Does this difference proceed from the greater quantity of nourishment necessary to support the large animals than the small, and from the former having a less proportional quantity of superfluous nutritive par- [255] ticles, capable of being converted into semen, than the former?  It is certain, that the small animals eat more, in proportion to their bulk, than the large.  But it is likewise probable, that the prodigious increase of the smaller animals, as bees, flies, and other insects, may be owing to the extreme fineness and delicacy of their organs and members, by which they are enabled to select the most substantial and most organic parts of the animals and vegetables, from which they extract their nourishment.  A bee, which lives upon the purest and most refined parts of flowers, receives from its food a greater proportional quantity of organic particles than a horse, who feeds upon hay, straw, and the grosser parts of vegetables.  The horse, accordingly, produces but one at a time, while the bee produces many thousands. The oviparous animals are, in general, smaller than the viviparous, and they are likewise much more prolific.  The long time that the foetus remains in the uterus of viviparous animals, is another obstacle to multiplication:  During gestation, and the suckling of the young, no new generation can take place. But the oviparous animals, which produce, at the same time, both uterus and foetus, and throw them out of the body, are almost perpetually in a condition to reproduce; and it is well known, that, if a hen be prevented from sitting, and be fully fed, the number of her eggs may be greatly increased.  If hens lay not while they brood, [256] it is because they cease to eat; and for this purpose they leave not their nests but once a day, and even then for a very short time, lest their eggs should be injured by the cold.  During this operation, they take not above one tenth part of their ordinary nourishment.

 

Animals which produce but one at a birth, acquire nearly their full growth before they are fit for generating.  But those which produce many, generate before they are half grown.  Man, the horse, the ass, the sheep, are incapable of generation till after they have nearly acquired the greatest part of their growth.  It is the same with pigeons and other birds that lay but a small number of eggs:  But those that are more prolific, as cocks and hens, fishes, &c. begin to generate much sooner.  A cock is capable of this operation at the age of three months, when he is not above one third of his full size.  A fish, which, in 20 years, will weigh 30 pounds, generates the first or second year, when it weighs not, perhaps, more than half a pound.  But experiments are still wanting to ascertain the growth and duration of fishes: Their age may be discovered by examining with a microscope the annual rings or strata of which their scales are composed.  But we are ignorant how far this may extend.  I have seen, in the Count de Maurepas’ ponds, carps which were well attested to be at least 150 years old, and they appeared to be equally active and lively as common carps. [257]  I will not say with Leeuwenhoek, that fishes are immortal, or, at least, that they cannot die of old age.  Every thing, in time, must perish.  Whatever has an origin, a birth, or commencement, must arrive at a termination or death.  But fishes, by living in a uniform element, and being sheltered from the injurious vicissitudes of the air, must continue longer in the same state than the other animals, especially if these vicissitudes, as Bacon remarks, be the chief causes of the destruction of animated beings.  But the principal cause of the longevity of fishes is, that their bones are softer than those of other animals, and do not perceptibly harden with age.  The bones of fishes lengthen, and turn thick without acquiring more solidity.  But the density of the bones of other animals continually increases; and, when their interstices are completely filled and obstructed, the circulation of their fluids ceases, and death ensues.  But, in the bones of fishes, this augmentation of solidity, which is the natural cause of death, proceeds in such an imperceptible manner, that they must live very long before they can feel any of the effects of old age.

 

All quadrupeds covered with hair are viviparous, and those covered with scales are oviparous.  The close texture of the shells or scales of oviparous animals prevents them from losing so much matter by transpiration, as makes its way through the porous skins of the viviparous.  [258]  May not this retention of superfluous nourishment, which cannot escape by transpiration, be one reason of the extraordinary fertility of these animals, and of their being able to subsist a long time without food?  All birds and flying insects are oviparous, except some species of flies which produce their young alive.*  These have no wings immediately after their birth; but they gradually shoot out as the animal advances in growth; and they are not in a condition to be used till it acquires full maturity.  All shellfishes are viviparous; and likewise those reptiles that have no feet, as snakes and serpents; they change their skins, which are composed of small scales.  The viper is but a slight objection to this general rule; for it is not properly viviparous.  It first produces eggs, from which the young are hatched:  This operation is indeed carried on and compleated [sic]  in the body of the mother; and, in place of laying the eggs, like other oviparous animals, the viper hatches them within the body.  The salamander, in which, as Maupertuis remarks,+ both eggs and young are found at the same time, is a similar exception in oviparous quadrupeds.

 

Most animals are multiplied and perpetuated by copulation.  But many animals, as the greatest number of birds, propagate rather by a kind of compression, than a proper copulation.  Some [259] birds, indeed, as the ostrich, the male duck, &c. have considerable members, and propagate by a real intromission.  Male fishes approach the females in the season of spawning.  They seem to rub their bellies against each other; for the male often turns on his back to meet the belly of the female.  But no actual copulation takes place.  The part necessary for this operation does not exist; and the males only approach the females for the purpose of shedding the liquor of their milts [sic] upon the eggs, which at that season drops from the females. The male seems to be more attached to the eggs than to the female; for, when she ceases to throw out the eggs, the male instantly abandons her, and follows, with ardor, the eggs which are carried down by the stream, or dispersed by the winds.  He passes and repasses a thousand times over every place where he finds eggs. It is not, surely, for the love of the mother that he makes all these movements:  He cannot even be supposed to know her; for he has been often seen shedding his semen promiscuously on all the eggs that came in his way, without having ever met with the female to which they belonged.

 

Thus some animals are distinguished by sexes, and endowed with members proper for copulation.  There are others which likewise have sexes, but want the necessary members. Others, as snails, have both members and sexes in each individual.  Others, as the vine-fretters [sic], have [260] no sexes, are equally fathers or mothers, and produce of themselves without copulation. Though they seem to copulate at pleasure, we are unable to discover the use of their junction, or whether it be really a sexual embrace; unless we should suppose Nature to have endowed this small insect with generative faculties superior to those of any other species of animals, and to have bestowed on every individual not only the power of reproduction, but likewise the power of multiplying by sexual communications.

 

But, whatever varieties take place in the generation of different species of animals, Nature prepares the body for it by a new production, which, whether it be external or internal, always precedes generation:  Immediately before the season of impregnation, the ovaria of oviparous animals, and the testicles of the females of the viviparous, undergo a considerable change.  The oviparous animals produce eggs, which gradually increase in size, till they quit the ovarium and fall into the canal of the uterus, where they receive their white, their membranes, and their shell.  This production marks the fecundity of the female, and without which generation could not be effected.  In viviparous females, in the same manner, one or more glandular bodies appear upon the testicles, which gradually grow under the membranes that covers them.  These glandular bodies increase, and pierce, or rather elevate the membrane of the testicle; and, when [261] they arrive at maturity, a fissure, or several little holes, appear at their extremities, through which the seminal fluid escapes, and falls into the uterus.  These glandular bodies are new productions, which always precede generation, and without which it could not be effected.

 

Males undergo a similar change before they are fit for the purposes of generating.  In the oviparous animals, the seminal reservoirs are filled, and sometimes the reservoirs themselves are annually renewed.  The milts of some fishes, and particularly of the calmar [sic], are renewed every year.  The testicles of birds, immediately before the season of their amours, swell to an enormous degree.  The testicles of the males of viviparous animals, especially of those which have seasons, likewise swell considerably; and, in general, the genitals of every species suffer an erection, which, though it be external and causal, may be regarded as a new production that necessarily precedes the faculty of generating.

 

Thus, in all animals, whether male or female, generation is always preceded by new productions; and, when there is properly no new productions, some of the parts swell and extend to a remarkable degree.  In some animals, not only a new production appears, but their whole bodies are renewed, before generation can be effected; as happens in the surprising metamorphosis of insects, which seems to be intended for no other purpose than to enable these ani- [262] mals  to propagate their species; for their bodies are sfull grown before they are transformed.  The insect, immediately before its transformation, ceases to take nourishment; and it has no organs proper for generation, no means of converting the nutritive particles, with which it abounds more than any other species of animals, into eggs, or a seminal fluid.  Hence the whole of this great surplus of nutritive particles at first unites and moulds itself into a form nearly resembling that of the original animal.  The caterpillar becomes a butterfly, because, having no organs of generation, no reservoirs for containing the superfluous nutritive particles, and, consequently, being incapable of producing minute organic bodies similar to the animal itself, the organic nutritive particles, which are always active, assume, by their union, the form of a butterfly, partly resembling that of a caterpillar, both internally and externally, excepting that the parts of generation are unfolded, and rendered capable of receiving and transmitting the nutritive organic particles which form the eggs, and individuals peculiar to the species.  The individuals produced by the butterfly ought not to be butterflies, but caterpillars; because it was the caterpillar that received the nourishment, and because the organic particles of this nourishment must therefore be assimilated into the form of a caterpillar, and not of a butterfly, which is only an occasional production of the superfluous [263] nourishment that precedes the real production of animals of this species, and a method employed by Nature to accomplish the important purposes of generation, similar to the production of glandular bodies, and of milts, in other animals.

 

When the superabundant quantity of organic nutritive particles is not great, as in man, and most large animals, generation does not take place till the growth of the body is nearly completed; and even their prolific powers are limited to a small number of young:  But, when these particles are more abundant, as in birds, and oviparous fishes, generation is effected before the animal be fully grown, and the production of individuals is very numerous. When the quantity of organic nutritive particles is still greater, as in insects, it first produces a large organized body, retaining the internal and essential constitution of the animal, but differing in several parts, as the butterfly differs from the caterpillar; and then it quickly generates an amazing number of young, similar to the animal that first prepared the organic nourishment from which they derived their origin.  Lastly, when the quantity of superfluous nourishment is very great, and when the animal, at the same time, possesses the organs necessary to generation, as in the vine-fretters, it first confers on each individual the power of generating, and then a transformation, like that which other insects undergo:  The vine-fretter becomes a flie [sic]; but [264] it can produce nothing, because it is only the residue of the organic particles that had not been employed in the production of the young.

 

Almost all animals, man excepted, have certain annual season appropriated to the purposes of generation.  To birds, spring is the season of love: Carps, and several other fishes, spawn in June and August.  Pikes, and some other fishes, spawn in the spring.  Cats have three seasons annually, in the months of January, May, and September.  The roe-deer rut in December, wolfs and foxes in January, horses in summer, stags in September and October; and almost all insects generate only during the autumn.  Some animals, as the insects, are totally exhausted by generation, and die soon after it.  Others, though they die not, become feeble, are much emaciated, and require a considerable time to repair the great waste of their organic substance.  Others are less affected, and are capable of frequently renewing their amours; lastly, man is very little affected, or, rather, he quickly repairs the loss, and therefore is, at all times, in a condition for propagating.  All these varieties solely depend on the particular construction of the animal organs.  The limits fixed by Nature upon the modes of existing are equally conspicuous in the manner of taking and digesting the food, in the means employed for retaining or throwing it out of the body, and in the instruments by which the organic particles [265] necessary to reproduction are extracted.  And, upon the whole, it is apparent, that every thing exists which can exist.

 

The times of the gestation of females are equally various:  Some, as mares, carry their young from eleven to twelve months; others, as women, cows, and hinds, carry their young nine months; others, as foxes and wolves, carry five months; bitches carry nine weeks, cats six weeks, and rabbits thirty-one days.  Most birds are hatched in twenty-one days; though some of them, as the thistle-finches, hatch in thirteen or fourteen days.  Here the variety is equally great as in every other part of the oeconomy [sic] of animals:  The largest animals produce fewer young, and carry them longest; which confirms the doctrine, that the quantity of organic nourishment is proportionally less in large than in small animals; for the foetus derives its growth and the expansion of its parts from the superfluous nourishment of the mother; and, as this growth requires longer time in large than in small animals, it is proof that the quantity of organic particles is not so great in the former as in the latter.

 

Animals, therefore, are much diversified as to the time and manner of gestation, of engendering, and of producing; and this variety originates from the very causes of generation. For, though the organic matter, which is common to every thing that lives or vegetates, be the gene- [266] ral principle of reproduction, the manner of its union, and the combinations it forms, must be infinitely varied, that the whole may become the sources of new productions.  My experiments clearly demonstrate, that there are no pre-existing germs, and that the generation of animals and vegetables is not univocal.  There are, perhaps, as many beings, which either live or vegetate, produced by a fortuitous assemblage of organic particles, as by a constant and successive generation.  It is to such productions that we ought to apply the axiom of the antients [sic], Corruptio unius, generation alterius. The corruption and resolution of animals and vegetables produce an infinite variety of organized bodies:  Some of them, as those of the calmar, are only a kind of machines [sic], which, though exceedingly simple, are very active.  Others resemble vegetables in their manner of growth and expansion.  There are others, as those of blighted wheat, which, at pleasure, can be made alternately to live or to die; and it is difficult to know to what they should be compared.  There are still others, and in great numbers, which are at first a kind of animals, then become a species of vegetables, and again return alternately to their vegetable state.  The more we examine this species of organized bodies, we shall probably discover greater and more singular varieties of them, in proportion as they [267] are farther removed from our observation, and from the structure of other animals with which we are already acquainted.

 

For example, blighted corn, which is effected by an alteration or resolution of the organic substance of the grain, is composed of multitudes of small organized bodies resembling eels.  When infused in water for ten or twelve hours, we discover them to have a distinct wreathing, and a small degree of progressive motion.  They cease to move as soon as the water fails them; and their motion commences upon the addition of fresh water:  This alternate death and reviviscence may be repeated for months, and even for years; so that these small machines may be made to act as long and as often as we please, without destroying or diminishing their force.  They are a species of machine, which begin to act whenever they are immersed in a fluid.  These filaments sometimes open like the filaments of the semen, and produce moving globules:  We may, therefore, conclude them to be of the same nature, excepting that they are more fixed and solid.

 

The eels in paste have no other origin than the union of the organic particles of the most essential parts of the grain.  The first eels which appear are certainly not produced by other eels; but, though they are not propagated themselves, they fail not to engender other living eels.  By cutting them with the point of a lancet, we dis- [268] cover smaller eels issuing in great numbers out of their bodies.  The body of this animal seems to be only a sheath or sac containing a multitude of smaller animals, which perhaps are other sheaths of the same kind, in which the organic matter is assimilated into the form of eels.

 

A great number of experiments would still be necessary to distinguish these animals, which are so singular and so little understood, into classes and genera.  Some of them may be regarded as real zoophytes, which enjoy a kind of vegetation, and which, at the same time, seem to wreath and move like animals.  Others appear, at first, to be animals, and then join and form a species of vegetables.  A small attention to the resolution of a single grain of corn will elucidate, at least in part, what I have said on this subject.  I might add other examples; but those I have given were only produced for the purpose of exhibiting the varieties of generation. There are unquestionably several organized bodies which we consider as real animals, but which are not engendered by others of the same species.  Some of them are only a kind of machines; and some of these machines have a certain limited effect, and act only for a certain time, as the machines in the milt of the calmar; others may be made to act as long and as often as we please, as those of blighted grain.  There are vegetables which produce animated bodies, as the filaments of the human semen, from which active globules issue [269] and move by their own powers.  In the corruption, the fermentation, or rather in the resolution of animal or vegetable substances, we find real animals capable of propagating their species, though they were not themselves produced in this manner.  These varieties are, perhaps, more extensive than we imagine.  Though it be right to generalize our ideas, to assemble the effects of Nature under one point of view, and to class her productions; yet numberless shades, and even degrees, in the great scale of being, will always escape our observation.

                                                                                                          

Notes

 

* See Leeuwenhoek, tom. 4. p. 91 [back to page 259].

+ Mem. De l’Acad. Annee 1727, p. 32 [back to page 259].