MORPHOGENESIS OF COMPOUND MELANOSOMES IN MELANOMA-CELLS OF A GRAY HORSE

A thoroughbred horse, gelding, gray color, aged 19 years old had cutan eous melanomas from the root to the middle of the tail, and throughout the connective tissues of the whole body. Histologically, the tumors were diagnosed as mature melanotic melanomas characteristically deposi ted with abundant melanin pigment. Examined with an electron microscop e, melanosomes were electron opaque without internal structure (stage IV), or as mature granular and lamellar types. Most of them were fused with each other, and formed compound melanosomes, which was similar t o internal melanin aggregates in shape. The internal melanin aggregate s gradually disintegrated, and compound melanosomes grew spherical. Th e compound melanosomes changed into autophagosomes.