The allantois is a membrane which is found in the foetus of the sow, mare, cow, and many other animals. This membrane adheres to the bladder of the foetus, and is said to be placed there for the purpose of receiving its urine while it is in the belly of the mother; and at the instant of birth, indeed, an inconsiderable quantity of liquor is found in the allantois; in the cow, where perhaps it is most abundant, it never amounts to more than a few pints; and the extent of the membrane is so great, there is not any proportion between that and the liquor. This membrane, when filled with air, forms a kind of double packet, in the shape of a crescent, thirteen or fourteen inches long, and from nine to twelve inches broad. Can it require a vessel capable of containing several cubic feet to receive three or four pints of water? The bladder of the foetus itself, if not pierced at the bottom, would suffice to contain this liquor, as it does in mankind, and those animals where the allantois has not been discovered; it is, therefore, plain this membrane is not designed to receive the urine of the foetus, nor for any purpose we are capable of imagining, for if it was to be filled it would form a bulk as large as the body in which it was contained; besides, as it bursts at the moment of birth, and is thrown away with the other membranes which envelop the foetus, it is certainly as useless then as it was before. The number of teats, it has been said, in every species of animals, corresponds with the number of young which the female can produce and suckle. Why then has the male, which never produces, usually the same number of teats as the female? and why should the sow, which sometimes produces eighteen or twenty pigs, never have more than twelve teats, and sometimes less? Does not this prove that it is not by final causes that we can judge of the works of Nature, and that we ought not to determine but by examining how she acts, and by employing the physical reasons which present themselves in the immense variety of her productions? Allowing that this method, which is the only one that can conduct us to real knowledge, is more difficult than the other, and that there are an infinity of facts in Nature, which, like the preceding, cannot be applied with success, instead of searching for the use of this great capacity in the allantois, we ought to inquire into those physical relations which may indicate the origin of its production; by observing, for example, that in animals, whose stomachs and intestines are not very large, the allantois is either very small or does not exist, and that consequently the production of this membrane has some connection with the size of the intestines, &c. By considering, in the same manner, that the number of teats is not equal to those of the young, admitting only that the most prolific animals have the greatest number of teats, we may conceive that this numerous production depends on the conformation of the interior parts of