Page:The Works of William Harvey (part 1 of 2).djvu/497

 said, the first effect of incubation is to cause dilatation of the cicatricula, and the formation of the colliquament, in which the blood first flushes and veins are distributed, and where the effects of the native heat and the influence of the plastic power first show themselves. And then, the more widely the ramifications of these veins extend, in the same proportion do indications of the presence of the vital power and vegetative force appear. For every effect is a clear evidence of its efficient cause.

In a word I say, from the cicatricula (in which the first trace of the native heat appears) proceeds the entire process of generation ; from the heart the whole chick, and from the um- bilical vessels the whole of the membranes called secundines that surround it. We therefore conclude that the parts of the embryo are severally subordinate, and that life is first derived from the heart.

EXERCISE THE FIFTY-FOURTH.

Of the order of the parts in Generation from an egg, according to Fabricius.

Having already determined what part is to be esteemed the first, the blood, to wit, with its receptacles, the heart, veins, and arteries, the next thing we have to do is to speak of the rest of the parts of the body and of the order and manner of their generation.

Fabricius, in whose footsteps we have resolved to tread, in speaking of the generation of the chick in ovo, passes in review the actions which take place in the egg, and by the effect of which the parts are produced, discussing them seriatim,) as if a clearer view were thence to be obtained of the order or sequence of generation. " There are three primary actions," he says, 1 which present themselves in the egg of the bird : 1st, the generation of the embryo; 2d, its growth; 3d, its nourish- ment. The first, or generation, is the proper action of the egg; the second and third, viz. growth and nutrition, go on

1 Op. supra cit. p. 41.