Abstract
Pyloric caeca of rainbow trout, Salmo gairdneri, Richardson were examined by light and electron microscopies.
The mucous membrane was composed of epithelium, lamina propria, stratum granulosum internum, stratum compactum (internum), stratum granulosum (externum), and stratum compactum externum.The stratum granulosum internum consists of a layer of slender cells containing a number of granules.In the space between the stratum granulosum (externum) and the tunica muscularis, a thin layer of compact collagen fibers (stratum compactum externum) and a layer of fibroblasts are recognized.The layer of collagen fibers is in contact with the stratum granulosum (externum), and the layer of fibroblasts with the tunica muscularis.
Pinocytotic invaginations and pits coated with less dense material are seen within the apical plasma membrane between the bases of the microvilli of epithelial cells.
A well-developed tubulo-reticular system, an extensive network consisted of the smooth and rough endoplasmic reticula, occupied the cytoplasmic area subjacent to the terminal web.Within cisternal profiles of the tubulo-reticular system, there often appeared small droplets of various electron densities which range about 70 to 140 mμ in diameter.
Two or three well-developed Golgi apparati formed a Golgi area in the supranuclear region.In the superjacent cytoplasmic region there often appeared round or oval membranebound bodies, perhaps a kind of cytolysomes, measuring approximately 4 to 5μ in diameter.
A relatively large number of sac-like or secretory granule-like bodies (or less dense bodies) are scattered within the cytoplasm.
Relatively well-developed lamellar membrane structures could be observed in the infranuclearcytoplasm, often connected with the peripheral (or lateral) plasma membrane.
Ampullae of Golgi lamellae, Golgi vacuoles, and the intercellular spaces contained numerous less dense vesicles 30 to 90 mμ in diameter.They were often seen also near thebasement membrane and the outside of capillaries, suggesting their transport from the epithelial cells toward the capillaries (or lacteals).
