The cell in development and inheritance . clei. Z). Approach of the nuclei. E. Unionof the nuclei. F. Cleavage-nucleus. nucleus and causing division of the o,^^ without itnion of the germ-nuclei, though the sperm-nucleus afterward conjugates with one ofthe nuclei of the two-cell stage. This process, known as partial fer-tilization, is undoubtedly to be regarded as abnormal. It affords,however, a beautiful illustration of the view that it is the centro-some alone that incites division of the egg, and is therefore the fer-tilizing element proper (Boveri, Zj, 2). The foregoing facts lead us to a
The cell in development and inheritance . clei. Z). Approach of the nuclei. E. Unionof the nuclei. F. Cleavage-nucleus. nucleus and causing division of the o,^^ without itnion of the germ-nuclei, though the sperm-nucleus afterward conjugates with one ofthe nuclei of the two-cell stage. This process, known as partial fer-tilization, is undoubtedly to be regarded as abnormal. It affords,however, a beautiful illustration of the view that it is the centro-some alone that incites division of the egg, and is therefore the fer-tilizing element proper (Boveri, Zj, 2). The foregoing facts lead us to a consideration of Boveris theoryof fertilization, which has for several years formed a central point ofdiscussion. The ground for this theory had been prepared by Oscar 1 Cf.^^. 181. 2 Cf. Kostanecki and Wierzejski, 96. PRELIMINARY GENERAL SKETCH 191 Hertwig and Fol. The latter (73) early reached the conclusion thatthe asters represented centres of attraction lying outside andindependent of the nucleus. Oscar Hertwig showed, in 1875, that. Fig. 97. — Fertilization of the egg of Nereis, from sections. ( X 400.)A. Soon after the entrance of the spermatozoon, showing the minute sperm-nucleus at (S, thegerminal vesicle disappearing, and the first polar mitotic figure forming. The empty spaces repre-sent deutoplasm-spheres (slightly swollen by the reagents), the firm circles oil-drops. B. Sperm-nucleus (cf) advancing, a minute amphiaster in front of it; first polar mitotic figure established;polar concentration of the protoplasm. C. Later stage; second polar body forming. D. Thepolar bodies formed; conjugation of the germ-nuclei; the egg-centrosomes and asters havedisappeared, leaving only the sperm-amphiaster {cf. Fig. 60). in the sea-urchin Qgg, the amphiaster arises by the division of asingle aster that first appears near the sperm-nucleus and accompaniesit in its progress toward the egg-nucleus. A similar observation wassoon afterward made by Fol (79) in the eggs of Astcrias an
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