Incorporation of Radioiodine into the Developing Endostyle of the Larval Lamprey

Incorporation of radioiodine (¹³¹I⁻) into small larvae of the Japanese river lamprey, 14 days after fertilization, was studied by radioautography. A small amount of radioiodine was incorporated into the larvae and became located in the mid-dorsal region of endostylar cells. The incorporation of radioiodine was greatest in endostylar cells near the junction with the anlage of the endostyle duct. It is possible that these cells form the anlage of the endostyle duct, which enters the endostyle.