Some observations on the fine structure of the enclostyle of larval lampreys, ammocoetes of Lampetra japonica

Abstract

The endostyle of larval lampreys, ammocoetes of Lampetra japonica was studied with the electron microscope. Type 1 cells in the dorsal as well as ventral lobules are characterized by a well-developed granular endoplasmic reticulum occupying most of the cytoplasm. Two kinds of cytoplasmic granules occur in type 1 cells: large less-dense and small dark. The dark ones, corresponding to the aldehyde-fuchsinopbile and aldehyde-thioninophile substances, are gathered in the cytoplasmic processes that terminate at the endostylar lumen. Both granules are apparently produced in the granular endoplasmic reticulum and Golgi apparatus system, and may be protein-secretory substances. The type 2 cells, cylindrical in shape, and with numerous cilia and microvilli, contain free ribosomes, glycogen particles, and a few lysosome-like dense bodies. In addition, the type 2c cells contain a few elements of granular endoplasmic retieulum. In the type 3 cell, the principal iodine-concentrating cell, cilia and microvilli are relatively fewer, and the granular endoplasmic reticulum is fairly well developed, and some of the elements of the endoplasmic reticulum are continuous with the Golgi zone. Small vesicles, which might be derived from the Golgi apparatus, are located in the apical part of the cytoplasm. These are considered to be secretory materials containing the thyroglobulin. A small number of glycogen particles are widely distributed. The immature or transitional type 3 cells, lying between type 2c and type 3 cells, are relatively low in height and contain free ribosomes and glycogen particles. There are very few elements of granular endoplasmic reticulum. The type 4 cell, which is characterized by a cytoplasmic process, has widely distributed glycogen particles and small vesicles. The granular endoplasmic reticulum and free ribosomes are scarce. The type 5 cells, forming the lining of the endostylar chamber, are flattened or cuboidal and contain numerous small smooth vesicles, glycogen particles, small dark granules and heterogeneous dense bodies, and lack cilia and microvilli. The elements of granular endoplasmic reticulum and free ribosomes are very few in all cells of this type.