. Comparative anatomy. Anatomy, Comparative. NUCLEUS Fig. 37.—Cleavage of egg of AMPHIOXUS. A, undivided egg; B, in process of first cleavage; C, four-cell stage, lateral view; D, four-cell stage, polar view; E, eight-cell stage, lateral view; F, sixteen-cell stage, lateral view; G, eighty-eight cells, lateral view; H, same stage as G, median section; I, later stage, lateral view. P, polar body. (After Hatschek.) cleavage continues (Fig. 37, G-I) until between two hundred and three hundred cells have been formed. This stage of the embryo is called the blastula. The name, blasto- coele, is appl
. Comparative anatomy. Anatomy, Comparative. NUCLEUS Fig. 37.—Cleavage of egg of AMPHIOXUS. A, undivided egg; B, in process of first cleavage; C, four-cell stage, lateral view; D, four-cell stage, polar view; E, eight-cell stage, lateral view; F, sixteen-cell stage, lateral view; G, eighty-eight cells, lateral view; H, same stage as G, median section; I, later stage, lateral view. P, polar body. (After Hatschek.) cleavage continues (Fig. 37, G-I) until between two hundred and three hundred cells have been formed. This stage of the embryo is called the blastula. The name, blasto- coele, is applied to the cavity. The second and third cleavages introduce inequality of size among the resulting cells. This inequality persists as cleavage goes on. It is correlated with the distribution of yolk in the protoplasm, the larger cells containing the more yolk. The cells of the blastula grade from minimum size at one pole (animal) of the sphere to maximum size at the opposite pole (vegetal). This Fig. 38.—Ovarian egg of Frog; median , .^ . ,, 1 • ,1 section. (Redrawn from Morgan, The Polanty IS established m the egg Development of the Frog's Egg; The before cleavage begins. Macmillan Co.) t * 1 ••l- o i • In Amphibians. Some amphi- bian eggs (not including the gelatinous envelope) are about 2 mm. in diameter. Such an egg would possess a volume about eight thousand YOUK. VEGETAL POLE. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son
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