. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 270 FERTILIZATION. Fig. 138. Polyspermy in the European newt, Triton, fAfter Fankhauser, '48.) (A) Ten minutes after insemination at 23° C. Metaphase of second maturation division; four sperm have entered the egg, one of which is at the vegetal pole of the egg, and another between the two poles of the egg. (B) One hour and 30 minutes; second polar body given off; small egg pronucleus moves toward nearest sperm nucleus. The latter will become the p
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 270 FERTILIZATION. Fig. 138. Polyspermy in the European newt, Triton, fAfter Fankhauser, '48.) (A) Ten minutes after insemination at 23° C. Metaphase of second maturation division; four sperm have entered the egg, one of which is at the vegetal pole of the egg, and another between the two poles of the egg. (B) One hour and 30 minutes; second polar body given off; small egg pronucleus moves toward nearest sperm nucleus. The latter will become the principal sperm nucleus. Observe that accessory sperm nuclei are enlarging and a sperm aster is developed relative to each. (C) Two hours and 30 minutes. Egg and principal sperm pronuclei in contact; maximum development of sperm asters. (D) Three hours. Fusion of egg pronucleus and principal sperm pronucleus. Accessory sperm nucleus nearest to fusion nucleus shows signs of degeneration. Accessory sperm asters remain undivided, while principal sperm aster has formed an amphiaster. (E) Three hours and 30 minutes. Metaphase of first cleavage; all accessory sperm nuclei degener- ating. (F) Four hours. Early telophase of first cleavage; remnant of accessory nuclei being pushed out of animal pole region by amphiastei and spindle of first cleavage division. fertilizin molecule plus the sperm then have the ability to unite with an egg receptor, and the union of the fertilizin-sperm complex with the egg receptor, releases the activating principle within the egg, which spreads "with extreme rapidity" around the egg cortex. The activating principle activates the egg as a whole, setting it in motion toward development. It is thought to work espe- cially upon the cortex of the egg, producing cortical changes, including the formation of a fertilization membrane. Further, it agglutinates or immobilizes all other sperm around the egg. Consequently, polyspermy may be hindered by this
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