. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. First period.—The im- pregnated ovum being de- posited, and the temperature being favourable, develop- ment commences. The \o changes always begin at the margins of the cica- tricula, which appear to be resolved into granules, which extend into the albumen and vitellus. The centre of the germ remains the same, the only appreciable difference is the enlargement of its circumference: (A, gives the natural size of the ovum.) Second period.—The germ is much larger, its margins are dispersed in numerous granules ; the centre
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. First period.—The im- pregnated ovum being de- posited, and the temperature being favourable, develop- ment commences. The \o changes always begin at the margins of the cica- tricula, which appear to be resolved into granules, which extend into the albumen and vitellus. The centre of the germ remains the same, the only appreciable difference is the enlargement of its circumference: (A, gives the natural size of the ovum.) Second period.—The germ is much larger, its margins are dispersed in numerous granules ; the centre is not yet affected by this tendency to molecular dispersion, but has undergone a notable modification. It changes its situation and begins to move towards the extremity of the ovum, leaving in the place which it for- merly occupied a train of globules; it now, to compare small things with great, bears some resemblance to a comet, the nucleus of which is represented by the centre of the germ; the tail, which is formed by the dispersion of the globules, is transparent, and the vitellus which it covers may be as distinctly seen through it as the fixed stars through the tail of a comet. Third period.—The nucleus of the germ (fig. 106, a), which has continued to change its Fig. 106. M &Wf«3. place, is arrived near the extremity of the ovum, but has not quite reached it. The tract which it has traversed is marked by an infinity of granules, which are then so much dissemi- nated that they extend al- most to the opposite extre- mity of the ovum. It is then that the kind of comet which it represents is seen at its greatest development, and with all the characters that have been indicated. The movement of the nucleus of the cicatricula authorizes the supposition that that body has not, at least at the earlier periods, a very intimate connexion with the vitellus. Fourth period.—The nucleus of the germ has not gone beyond the point which it had attained, but it presents a ne
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