arise the sides, and the bones are distinguishable from the flesh by minute lines of extreme whiteness ; in the head three bullae are perceived, full of crystalline fluid, which corre- spond to the brain, the cerebellum, and one eye, easily observ- able by a black speck ; the substance which at first appears a milky coagulum, afterwards gradually becomes cartilaginous, has spinous processes attached to it, and ends in being com- pletely osseous ; what was at first of a mucous nature and co- lourless, is converted at length into red flesh and parenchyma ; what was at one time limpid and perfectly pure water, presently assumes the form of brain, cerebellum, and eyes. For there is a greater and more divine mystery in the generation of ani- mals, than the simple collecting together, alteration, and com- position of a whole out of parts would seem to imply ; inasmuch as here the whole has a separate constitution and existence before its parts, the mixture before the elements. But of this more at another time, when we come to specify the causes of these things,
EXERCISE THE FORTY-SIXTH.
Of the efficient cause of the generation of the chick and foetus.
We have thus far spoken of the matter from which the chick in ovo is generated. We have still with Fabricius to say a few words on the efficient cause of the chick. As this subject is surrounded with difficulties, however ; as writers nowhere else dispute more virulently or more wordily, and Aristotle himself in explaining the matter is singularly intricate and perplexed, and as various questions that can by no means be lightly treated do in fact present themselves for consideration, I conceive that I shall be undertaking a task worthy of the toil if, as I have done in the disquisition on the "matter," I set out here by stating in how many ways anything can be said to be " effi- cient " or " effective." We shall thus obtain a clearer idea of what it is which we are to inquire after under the name of " efficient," and further, what estimate we are to form of the ideas of writers upon this subject ; it will at the same time ap-
