fact, except the conception itself. I can only find, as I before said, a process of the bladder, situated between the umbilical arteries, which contains an excrementitious matter, and varies in length in different animals. Wherefore, in my opinion, the tunic which Fabricius calls the allantois is, in fact, the chorion; and the ancients applied the name of allantois to it on account of its resemblance to a double intestine. For that external membrane, constricted in the middle, and resembling a saddle-bag in form, which is stretched upwards to each horn of the uterus, and in its passage is pinched in by that part of the uterus which connects the horns, is in truth the chorion; and in the sheep, goat, roe, fallow-deer, and other cloven-footed animals, it can be raised by the hand in the middle of its course, and easily extracted whole; this is the same as what is called the "conception" or ovum. Like an egg, it contains within itself two fluids, and the fœtus with its appendages; it is possessed besides of those characters which Aristotle attributes to the egg; these are, that out of part of it the embryo is originally formed, and that the remainder constitutes the sustenance of the new animal, as has been frequently explained. I believe, then, the tunic which Fabricius called the allantois to be either the chorion or else some unnatural structure formed out of the reduplication of the membranes. It is accordingly only found to exist in some animals, and not always in these; it cannot be traced from the commencement of conception, and in some animals it is more apparent than in others: whilst in others nothing can be seen except a mere process of the bladder. Besides, Fabricius himself allows that its purpose is not to envelope the fœtus, but to contain its urine. In truth, I must think that he has described it rather to defend the doctrine of the ancients, than because he really believed he had discovered such a membrane, or that it served any good purpose. For he allows, with the ancients, and every medical school, that the chorion contains urine, when he says[1] that there are two humours encircling the fœtus, one, viz. in the amnion, consisting of sweat; the other in the chorion, consisting of urine. It is, therefore, clear that the ancients under the two names understood one and the same membrane; and that in
- ↑ Cap. i.
