ABSTRACT. In the present work the haemocytes of mussels Mytilus galloprovincialis (Mollusca, Bivalvia) have been studied by light and electron microscopy in order to describe their main morphological features and to relate these to their roles in immune defence. The haemocytes belong to two definitive differentiated types, hyalinocytes and granulocytes. The former shows the presence of several fine pseudopodial protrusions, large nucleus with clumps of dense chromatin, scant cytoplasm, a well developed Golgi apparatus, lysosomes, several mitochondria (some with characteristic inclusions), coated pits and peripherally placed membrane-bound endocytic vesicles, considerable amounts of endoplasmic reticulum and ribosomes. The granulocytes generally possess an organelle-free ectoplasmic zone, numerousmembrane-delimiteddense granules of various types, coated pits and vesicles, endocytic and phagocytic vesicles, multivesicular bodies, several peroxisome-like organelles, mitochondria with inclusions, scant endoplasmic reticulum and small Golgi apparatus. These cells show the presence of few lipid droplets and variable amounts of glycogen particles. Someof the substructural features of the granules are documented here to indicate their probable biogenesis, growth and relationship with the endolysosomal compartment. In addition, in vitro phagocytosis experiments demonstrate that both hyalinocytes and granulocytes uptake latex and zymosan particles, granulocytes being muchmore active in phagocytosis than hyalinocytes.

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The present transmission electron microscopic study of the spermatheca of a common Indian grasshopper, Gesonula punctifrons, has highlighted the presence of the glandular secretory cells (SaC) and ductule cell (DC) in the spermathecal epithelium and additionally the occurrence of muscle cells, tracheoles and haemocytes. Both the former cell types are secretory in nature and probably their discharges in the lumen of the cuticle-lined sperrnathecal duct or ductule vary in their chemical nature. The ultrastructural evidence gives ample support to a concept of a lysosomal control of the secretory materials prior to their liberation in the lumen. The characteristic features of the plasma membranes of the secretory cells clearly suggest their involvement in the transepithelial transport of ions and smaller molecules across the basement membrane. A neuronal supply to the sperrnathecal wall is yet to be demonstrated to explain the filling in and out of the male gametes by this organ.