Echinoderms of Connecticut (1912) Echinoderms of Connecticut echinodermsofcon00coew Year: 1912 to FIG. 15. Cleavage of egg of Sea-urchin, i, egg from ovary; 2, mature egg with the two minute polar bodies; 3, fertilization; 4 to 6, first cleavage, forming two blastomieres; 7, 8, second cleavage, with 4 blastomeres; 9, 10, third cleavage, with 8 blastomeres; n, fourth cleavage, with 16 blastomeres; 12, section of blastula. The blastula soon becomes covered with cilia and swims actively about in the water. (After Wilson.)

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