manner. Thefe productions, fo monftrous and fo uncouth in appearance, are not on that account the less subject to the conftant and general law of nature, that each animal produces its like. If we often fee infects of the fame species, proceeding from animals of a very different kind, it is not that the latter have generated the former; but the females of the one having introduced their eggs into the bo dies of the others, the young have been produced from these eggs, and after having fed on the fubftance of the animal in whofe body they were inclofed, iffue from it in the form of the infects that had placed them there. Thefe are facts now univerfally known, and which I have verified by experiments not neceffary here to be detailed.

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They cannot repair the lofs. This appears fo certain, and is fo conformable to the ideas we have of the formation of organifed bodies, that one would not expect to find exceptions to the rule. But the author of nature, whose wildom confounds all our reafoning, in order, as it would feem, to fhew us how little we ought to depend on our own powers when we judge of his operations, has created animals which form a very remarkable exception to it, having the fingular faculty of reproducing their members whenever they are deprived of them. Sea ftars, crabs and lobsters are instances of this, which cannot now be doubted, after what has been related by a naturalift of fuperior abilities, in the Memoirs of the Royal Academy of Sciences, for the year 1712.

But thefe inftances, and others which I might mention, by no means affect Mr Leffer's reafoning. It is not the fea ftar, the crab or the lobfter that replace the limb they have loft; it is nature which gives it to them, and they contribute as little to the reproduction as we do to that of our nails or our hair.

PAGE 30, 1. 3.

They multiply by generation. It is a general law of nature that animals preterve their fpecies, and multiply in the way of generation. This has never been doubted as to the larger animals, and when infects have been narrowly examined, it has been found that even they whofe production feemed the most equivocal, owe likewife their origin to the u nion of a male and female of the fame fpecies. But however general this rule may be, the univerfality of it is not

yet

yet established. The various ways in which propagation is feen to take place among infects, feem to authorize a doubt on this fubject. There are feveral forts of those animals formerly claffed among infects, fuch as fnails and earth-worms, which are both male and female in one individual. We find among true infects certain fpecies, the greater part of which are neither male nor female, as bees, wafps and ants. Some are obferved to engender without coupling, the male contenting himself with depofiting his femen on the eggs of the female, as in the Ephemera. Some are found which can produce a pofterity for feveral generations by a fingle embrace, as I have difcovered to be the cafe with the aphides. If we believe Swammerdam on this head, who however gives no folid proof of his opinion, there are fome females among infects which can be impregnated by the mere fmell of the male. All thefe various methods of propagation, lead us to prefume that there may be infects which multiply without reciprocal intercourfe, and without the procefs of generation ftrictly fo called, and where a single individual, by the exertion of its own powers, is fufficient to propagate its kind; but hitherto no author as far as I know, has demonstrated the fact by a conclufive experiment. It is true that Leewenhoeck and Ceftoni thought they had discovered fuch a one among the aphides. Neither they, nor M. de Reaumur ever faw them coupling, or could difcover a male one among the whole fpecies; all they examined whether winged or not, were always females, and with young even before they had attained their natural fize. Thefe experiments feemed pretty decifive, and others made by me feem ftill more fo. Some aphides, taken away at the moment of their birth, and kept fecluded under glaffes, in eight or ten days produced young. Thefe young were likewife inftantly removed, and bred up in the fame folitude, produced others nearly after the fame period, and that production continued long enough to perfuade me, by reafons ftronger than thofe of Leewenhoeck or Ceftoni, that their opinion was the true one. But having continued my experiments till the feafon when the leaves began to fall, and not having any farther doubt on the fubject, I was all at once undeceived, when I leaft expected it. I had collected all the young which my folitary aphides had produced, and had established a little colony of them on the extremity of the branch of a willow which I kept fresh in a glafs of water. The cold had already made the leaves to wither; but feveral of the aphides in the

002

nymph

nymph ftate, maintained themfelves on it with the reft, and arrived at their perfect form. One day as I was visiting them according to cuftom, I found one of thofe with wings, fitting on one without wings. I confidered this pofition at first as the effect of chance, but the tranquillity of the winged aphis, while the other, difturbed at my approach, was running up and down, made me fufpect fomething. I took a magnifying glafs, and upon a near examination, found that the. pofterior part of the winged infect, bending down towards that of the other, was intimately connected with the under part of it, and exhibited marks of an union in the common form. This attachment lafted more than an hour, after which the winged infect flew away. I faw the fame thing happen to many others of the colony, who formed a connection like the firft; and what perfuaded me that it was a true connubial intercourfe was, that having accidentally crushed two of them in that fituation, while I was examining two others, I found after their death, the extremities of their abdomen ftill attached. The notion therefore of there being animals which can individually propagate their fpecies is not yet established by experiments made on the aphides; let us fee if it is better founded on those that have been made on the mufcles of fresh waters.

Monfieur Mery in the Memoirs of the Royal Academy of Sciences for the year 1710, afferts that it is. He has obferved four parts in this animal that may ferve for generation: two of these he calls ovaria, because they contain eggs, and two he calls veficula feminales, becaufe in his opinion they contain the femen, which is white, and of the appearance of milk. Their ftructure appears fimilar, all four terminate in the anus, where he fays that the two principal ones, as they go out, are united, which is fufficient for generation; and as he has obferved in this animal, neither male nor female organ, he thinks himself the more authorized to conclude that it is androgynous. But this reafoning, however just it may feem, it is not fo conclufive as M. Mery. imagines. The parts which characterife the fexes, may be fo difguifed by their flexibility, by their fituation and form, in an animal whefe figure is fo anomalous as the muscle, that it is not impoffible but he may have feen them without knowing them; and even though they were actually not to be found, it would not prove that each mufcle was of both fexes. Neither male nor female organ is to be observed in the greater part of filhes, but are they on that ac

count

count both male and female? Befides, though two veffels of the four which terminate in the anus of the mufcle, are receptacles of its eggs, it does not follow that the other two are the refervoirs of the femen. The milky fluid they contain, may be deftined to another ufe, than that of fructifying the eggs; it may ferve to fix them to the bodies on which the animal depofits them; to envelope them with a fubftance which may defend them against the immediate action of the water, to afford the young, upon iffuing from the egg, a fuitable aliment. The eggs of many aquatic infects are furrounded with a clammy matter which they probaoly owe to fuch veffels. The glue which makes the eggs of butterflies adhere to the bodies on which we fee them fixe, proceeds from two veffels terminating in the rectum, and containing a vifcid humour, which is any thing but femen; why then thould thofe of mufcles contain it? But even tho' they fhould contain it, would it follow that nufcles were individually fuffic.ent for their own multiplication? By no means. The female butterflies have receptacles which contain femen, and that femen alone is able to fecundate their eggs; thefe receptacles alfo terminate in the rectum, and inundate the eggs in their paflage. But notwithstanding this,thefe butterflies must enjoy the company of the male, for it is the male alone who furnishes this femen. May this not alfo be the cafe with the river mufcles?

If it were certain that the pholades never leave the hole they form for themselves at the inftant of their birth, as M. de Reaumur maintains, on very plaufible grounds Mem. of the Royal Academy of Sciences 1712) one would be tempted to believe that thefe thell-fish were fufficient of themfelves for procreation, if we did not rather chufe to fuppose that their impregnation took place while they were yet in the matrix of their mother, a circumftance we are not hitherto acquainted with an inftance of; or perhaps that they have males of another form, and more active than themfelves, which vifit them in their retreats, as it happens to the gall infects. But if facts fo fingular as that in question, could be established by mere reafoning, no animal would better deferve to be put among the number of those which are fufficient of themselves to multiply the fpecies than that worm of the human body called Tania, the longest perhaps of all animals, fince fome of them have been found eighty yards in length, and it is not certain but that fome of them may be

ftill longer. This animal according to various authors is folitary, and, as they pretend, is formed in the human fœtus before it is born: it grows up with the perfon, and there is never more than one found in the body it inhabits. If thefe circumftances be true, as Hippocrates and his followers affert, what are we to believe concerning the origin of fuch an animal? For there have never been found, out of the bodies of animals, any thing fimilar to them, from which we might prefume they were derived and if there had, either great or fmall, their flat, thin figure, and the vaft multitude of articulations they are compofed of, would certainly have made them be taken notice of. It must therefore be admitted that thefe worms are only produced from thofe that are found in animal bodies; and if fo, how could they be generated but on the fuppofition that each fingly is fufficient of itfelf to produce its like, being always found folitary? and thus we have an inftance of our hermaphrodites in the Tania.

I know that this fuppofition does not remove all the dif ficulties attending the origin of this fingular worm. It may ftill be asked why it is always found fingle, and by what means its eggs or its young enter the body of another perfon? But it would not be difficult to answer these questions by new fuppofitions. The firft difappears by fuppofing that this worm is among the number of thofe that devour one another, the ftrongeft, having eaten up all thofe produced along with it in the fame place, muft neceffarily remain alone. As to the other difficulty we have only to suppose that the egg or the foetus of this worm is extremely small, and that the animal depofits it in our chyle, which it may do easily, if the orifice of its ovary is fituated near its head, as that of the fnail is. From the chyle it will enter into the mafs of blood; if it inhabits a woman, the communication her blood has with the foetus in her womb will introduce the egg or the fœtus of the worm into it by means of the circulation, and the egg and fœtus will begin to grow as foon as it arrives at the place deftined for its habitation. If it is harboured in the inteftines of a man, then the egg entring the mafs of blood, will be carried by the circulation. into the veffels where that blood is elaborated, and prepared for a purpofe neceffary to the prefervation of our fpecics; and thus we fee eafily how it may be mingled with the particles, which enter into the compofition of the human fœ

tus.