EXERCISE THE TWENTIETH.
The sixth inspection.
Everything is still more distinct upon the seventh day, and the rudiments of several of the particular parts are now conspi- cuous, viz., the wings, legs, genital organs, divisions for the toes, thighs, ilia, &c. The embryo now moves and kicks, and the form of the perfect chick is recognizable ; from this time for- ward, indeed, nothing is superadded ; the very delicate parts only increase in size. The more the parts grow the more is the albumen consumed, and the external membranes united come to be of the nature of the secundines, and ever more and more closely represent the umbilical cord. Wherefore I con- ceive that, from the seventh, we may at once pass on to the tenth day, nothing of any moment occurring in this interval which is not particularly noted by other writers, especially by Aristotle.
It happens, nevertheless, that when a number of eggs are examined together, some are found more precocious and forward, having everything more distinct ; others, again, are more slug- gish, and these have the parts less apparent. The season of the year, the place where the incubation is carried on, the sedu- lousness with which it is performed, and other accidents, have undoubtedly great influence on this diversity of result. I re- member on one occasion, on the seventh day to have seen the cavity in the blunt end enlarged in a sluggish egg, the colli- quament covered with veins, the vermicular embryo in its mid- dle, the rudiments of the eyes, and all the rest as it is met with in the generality of eggs on the fifth day ; but the pulsatory vesicles were not yet apparent, nor was the trunk or root of the veins from which we have said that they originate, yet to be discovered. I therefore regarded this egg as of a feeble nature and left behind, as possessed of an inadequate reproductive faculty, and near to its death ; all the more when I observed its colliquament less pellucid and refractive than usual, and the vessels not of such a bright red colour as wont. When the vital spirit is about to escape, that part which is first influenced in
