Cleavage - Representative Stages

Shown below are representative pictures of various cleavage stages in L. variegatus. Note that the first two cleavages are meridional, i.e. the cleavage furrow passes through the animal and vegetal poles. The next cleavage is equatorial, i.e., it passes through the embryo's midsection. The fourth cleavage is unequal (see next page).

L. variegatus zygotes, viewed from the side. A. 1-cell zygote. The fertilization envelope is visible as a large "halo" around the embryo. The arrow points to the site of sperm penetration. B. 2-cell. C. 8-cell. D. 16-cell. E. 32-cell. F. Hatched blastula (F is courtesy Dr. Chuck Ettensohn, Carnegie-Mellon Univ.).