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Definition: "A Y-shaped array of unicelluar glands on the top of the head, the open end of which faces anteriorly, that secrete an enzyme that dissolves or weakens the egg jelly and facilitates hatching. Presumptive cells of the hatching gland are present by the end of gastrualtion (NF stage 12.5) and differentiated cells start to form after neurulation is complete (NF stage 21)."