. The biology of the frog . through the first or secondcleavage furrows, producing thus a bilateral arrangement ofthe cells. The fourth cleavage furrows are subject to morevariation at the vegetal pole of the egg, and the subsequentdivisions soon become so irregular that it is impossible totrace out any plan of procedure. A fifth cleavage occurstypically parallel to the third, appearing first in the upperhemisphere and then in the lower. The cleavages thus farv^viaUy follow the rule that each cleavage plane comes in atright curgie-; to the previous cleavage plane. Deviationsfrom the typical me
. The biology of the frog . through the first or secondcleavage furrows, producing thus a bilateral arrangement ofthe cells. The fourth cleavage furrows are subject to morevariation at the vegetal pole of the egg, and the subsequentdivisions soon become so irregular that it is impossible totrace out any plan of procedure. A fifth cleavage occurstypically parallel to the third, appearing first in the upperhemisphere and then in the lower. The cleavages thus farv^viaUy follow the rule that each cleavage plane comes in atright curgie-; to the previous cleavage plane. Deviationsfrom the typical method of cleavage are apparently of littlemoment, even in the first few divisions, as such abnormallydividing eggs may nevertheless produce perfect embryos. Cleavage takes place more rapidly in the dark or animalpole, since at that place the protoplasm is most dense. Yolk,which is most abundant in the white or vegetative side of theegg, delays cell division, and we find in the later stages of 92 THE BIOLOGY OF THE FROG B
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