Histological observations on some of the endocrine glands in the remora, Echeneis naucrates L., caught off the coast of Sado Island in the Japan Sea.

Endocrine organs, such as the hypophysis, thyroid, endocrine pancreas, ovary and testis, of two specimens of the remora, Echeneis naucrates, were studied histologically to gain some knowledge about comparative anatomy and systematics. The specimens, one female and one male, were caught off the coast of Sado Island in the Japan Sea. Among four components of the hypophysis, the well developed pars intermedia (PI) is the largest and located in the ventral region of the gland. The PI consists chiefly of two types of glandular cells which are stained distinctly by a combination of dyes. The prolactin, adrenocorticotropic, gonadotropic, somatotropic and thyrotropic cells are also differentiated in the pars distalis. The thyroid gland, as a compact mass, indicates a fairly hyperactive state. The Brockmann body is composed mainly of three types of cells: A, B and D cells. It is characteristic of this species that each endocrine cell of the body gathers to form large clusters. Both ovary and testis were spent, but a number of young germ cells in various developmental stages were seen. The systematic position of the remora is discussed in comparison with other bony fishes.