miracles; and the parts are commenced, not by change of place, but by alteration in softness, hardness, temperature, and the other differences observed in similar parts, these being now actually made, which had before existed only potentially."
This is, in nearly so many words, the opinion of Aristotle, which supposes that the foetus is formed from the seed by mo- tion, although it is not at present in communication with the foetus, but simply has been so at a former time : his reasonings are, indeed, ingenious, and carefully put together, and from what we see in the order of the generation of parts, not im- probable. For the heart, with the channel of the veins, is first noticed as an animate principle, in which motion and sense reside ; or, as it were, an emancipated son, and a genital part, whence the order of the members is delineated, whence all things pertaining to the completion of the animal are dis- posed, and which has all the attributes bestowed upon it by Aristotle.
But it seems impossible, that the heart should be formed in the egg by the seed of the male, when that seed neither exists in the egg, nor touches it, nor ever has touched it ; because the seed does not enter the uterus where the egg is, (as is allowed by Fabricius,) nor is in any way attracted by it ; nay, even the maternal blood is not in the egg, nor any other prepared mat- ter, out of which the seed of the male may form this genital part, the author of all the others. For it is not immediately after coition, while the seed still remains within the body, and is in communication, that any part of the chick exists in the egg, but after many days, when incubation has taken place. More- over, in fishes, when the geniture of the male does nothing but touch the eggs externally, and does not enter into them, it is not likely that it performs any more ample functions when the agency is external, than does the seed of the cock in the already formed eggs of the hen. Besides, since immedi- ately after coition no trace of the egg as yet exists, but it is afterwards generated by the hen herself (I am speaking of the prolific egg) ; when now the seed of the cock is departed and vanished, there is no probability that the foetus is formed in that egg by the aforesaid seed, through means of one or any number of successive motions.
Nor indeed does the difference between prolific and unpro-
