CELLULAR DIFFERENTIATION IN THE URINARY BLADDER OF A EURYHALINE MARINE FISH, GILLICHTHYS MIRABILIS, IN RESPONSE TO ENVIRONMENTAL SALINITY CHANGE.

The urinary bladder of a euryhaline marine teleost, Gillichthys mirabilis, was studied by light and electron microscopy. An enlargement of the mesonephric ducts forms a sac-like structure lined by an epithelium composed of two major cell types. Tall columnar cells continuous with the duct epithelium are characterized by a large number of mitochondria and well-developed rough and smooth endoplasmic reticulum. Tubular smooth endoplasmic reticulum is more developed in the basal cytoplasm and often opens into the extracellular space. A second cell type, the low cuboidal cells, forming most of the bladder epithelium, has fewer mitochondria. Basal cells are rarely observed and mucous cells are absent. In seawater Gillichthys, cells of both types are separated by narrow intercellular spaces. In 5% seawater fish, the columnar cells show functional activation, as evidenced by an increased number of mitochondria and more extensive tubular smooth endoplasmic reticulum. No such changes were noted in the cuboidal cells; however, the lateral intercellular spaces are dilated probably owing to hypotonicity of the urine in the hypotonic environment. A functional difference between the two cell types is strongly suggested. The columnar cells may be responsible for active sodium uptake in hypotonic seawater environments.

Ultrastructural study of the relations between Leptomonas oncopelti (Noguchi and Tilden), protozoa trypanosomatidae, and the rectal wall of adults of Oncopeltus fasciatus dallas, hemiptera lygaeidae.

A laboratory colony of Oncopeltus fasciatus was found to be infected by Leptomonas oncopelti. The flagellates form a carpet attached to the cuticular intima of the rectal glands of adult bugs. The epithelial cells of these glands are characterized by infolded apical plasma membranes associated with mitochondria; the overlying cuticular intima shows endocuticular canals. The Leptomonas are attached by hemidesmosomes, located most often at the tip of the flagella. The Protozoa multiply by budding and the resultant straphangers cling to the parental flagellum. Adhesion of the flagellates to the cuticular lining is so strong that detaching flagellates carry with them the outer part of the epicuticle. Epicuticle repair presumably occurs through the endocuticular canals.