Name: 56-cell stage
ECAO ID: 0000220
Definition: "An embryo that is composed of 56 cells and is surrounded by a fertilization envelope. Note for euechinoid indirect developers: In the animal hemisphere, cells of the an1 and an2 tiers underwent an additional meridional division, producing tiers composed of 16 cells. The macromeres divided equatorially and equally, generating two vegetal cell tiers, each composed of 8 cells of equal volume, namely the veg1 tier (located below an2) and the veg2 tier (located below veg1 and above the large micromeres). At that stage, the large and small micromeres (4 cells each) have not undergone yet a sixth division."
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