The distribution of melanosomes in larvae reared from normal and from pigmentless eggs of Xenopus laevis

The distribution of pigment granules or melanosomes in tadpoles of Xenopus laevis reared from phenylthiourea (PTU)‐induced pigmentless eggs is compared with the distribution of melanosomes in tadpoles from normal eggs. Some animals from each group were raised in a solution of PTU. It is concluded that melanosomes observed in the central nervous system, liver, epidermis, oral sucker, gut, notochord, and early eye of normal larvae originate in the oocyte. Those in the brain ventricles become engulfed by macrophages. Melanosomes do not appear in these tissues of early tadpoles reared from pigmentless eggs; however, pigment is later synthesized in dermal, meningeal, and peritoneal melanocytes as in the normal larvae. Since the synthesis of new melanin is blocked in embryos reared in PTU, tadpoles derived from pigmentless eggs and reared in PTU are completely devoid of melanosomes.