554 THE MEMBRANES
the cloven-footed animals they called it " allantois," on account of its form; but in others "chorion," because they thought its object was to receive the urine. Wherefore they allow that this tunic is neither found in man nor any of the other animals. For what need can there be of another tunic to retain the urine, when they themselves admit that the office of doing so belongs especially to the chorion ? There can be no probable reason as- signed why this tunic should exist in the sheep, goat, and the other cloven-footed animals, and not also in the dog, cat, mouse, and others. For in truth, if the object of this membrane were to contain the urine, the foetus of the sheep and cow must secrete a much larger quantity than those of animals furnished with in- cisors in both jaws ; there must then either be three different humours, or at least two receptacles for the urine. For myself, I am sure that the chorion from the first is full of water. I will not, however, enter into controversies; I would rather record what I have found by my own observations.
To do as Fabricius has done, and give the structure of the full-grown and perfect embryo, is one thing, but it is another to enter fully on the subject of its generation and first formation : just as they are very different things to describe the ripe fruit of an apple or any other tree, and to explain the manner in which it is produced from the germ. I will, therefore, briefly go through the stages by which the " conception" is brought to maturity, in which way the true doctrines in the matter of the membranes and other foetal appendages will be better ascer- tained.
In the production of all living creatures, as I have before said, this invariably holds, that they derive their origin from a certain primary something or primordium which contains within itself both the " matter" and the "efficient cause/' and so is, in fact, the matter out of which, and that by which, whatsoever is produced is made. Such a primary something in animals (whe- ther they spring from parents, or arise spontaneously, or from putrefaction) is a moisture inclosed in some membrane or shell; a similar body, in fact, having life within itself either actually or potentially ; and this, if it is generated within an animal and remain there, until it produce an "uni vocal" (not equivocal) animal, is commonly called a " conception;" but if it is ex- posed to the air by birth, or assumes its beginning under other
�� �
