Page:The Works of William Harvey (part 1 of 2).djvu/344

 first day of the incubation to the fifth \ from thence on to the tenth or fourteenth : and from this or that to the twentieth. It seems as if he had only given an account in his history of the circumstances he observed at these three epochs ; and it is then indeed that the greatest changes take place in the egg ; as if these three critical seasons., or these three degrees in the process which leads from the perfect egg to the evolution of the chicken, were especially to be distinguished. On the fourth day the first particle of the embryo appears, viz. : the punctum saliens and the blood ; and then the new being is incorporated, On the seventh day the chick is distinguished by its extremities, and begins to move. On the tenth it is feathered. About the twentieth it breathes, chirps, and endeavours to escape. The life of the egg, up to the fourth day, seems identical with that of plants, and can only be accounted as of a vegetative nature. From this onwards to the tenth day, however, like an animal, it is possessed by a sensitive and motive principle, with which it continues to increase, and is afterwards gradually perfected, becoming covered with feathers, furnished with a beak, nails, and all else that is necessary to its escape from the shell ; emancipated from which, it enters at length on its own inde- pendent existence.

Of the incidents that happen after the fourth day, Aristotle enumerates three particularly, viz. : the construction of the body ; the distribution of the veins, which have already the office and nature of the umbilicus ; and the matter whence the embryo first arises, and is constituted and nourished.

In reference to the structure of the body, he speaks of its size and colour, of the parts which are most conspicuous in it, (the head and eyes,) and of the distinction of its extremities.

The body is indeed extremely minute, and of the form of the common maggot that gives birth to the fly ; it is of a white colour, too, like the maggot of the flesh-fly which we see che- rished and nourished in putrid meat. He happily adds, " it is most remarkable for its head and eyes." For what first appears is homogeneous and indistinct, a kind of concretion or coagu- lation of the colliquament, like the jelly prepared from harts- horn ; it is a mere transparent cloud, and scarcely recognizable, save as it appears, divided, seemingly, into two parts, one of which is globular and much larger than the other ; this is the