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Effect of shikonin, tapa and ecdysone was studied on the activity of alkaline phosphatase by biochemical and histochemical methods. Tepa and shikonin (sterilants) inhibited the enzyme activity while ecdysone slightly increased the activity. This behaviour has been discussed in the present paper.

The saccus vasculosus of Cyprinion macrostomus is made up of coronet and supporting cells. Neurones are not observed. The luminal surface of the coronet cells exhibits hair-like protrusions. The saccus vasculosus is mainly concerned with a secretory function. Plenty of secretory material is seen in the lumen. PAS and alcian blue tests are positive for the secretory material in the lumen and the apical protrusions of the coronet cells. Some cells also exhibit small PAS- and alcian blue-positive granules. The possibility of the elaboration of glycogen by the coronet cells is ruled out. The toluidine blue test is also positive for the secretory material in the lumen and the apical protrusions. Small metachromatic granules are also seen in some of the coronet cells. The acetone-Sudan black B and Sudan black B tests point to lipid moiety of the coronet cells, the apical protrusions and the secretory material in the lumen. The acrolein-Schiff and ninhydrin-Schiff tests point to a protein moiety of the coronet cells and the secretory material in the lumen. The performic acid-alcian blue test showed cystine to be present in small amount.

The giant neurosecretory cells in the thoracic ganglion of the adult and juvenile crab, Potamon magnum magnum (Pretzman) were histochemically investigated. The secretion is mainly proteinaceous in nature, containing considerable amounts of acid mucosubstances, sulphate esters, lipids and a little carbohydrate but no glycogen. The detailed nature of proteinaceous neurosecretory material in the adult crab was further tested. It appears that the neurosecretory material of these cells contains moderate amounts of sulfhydryl groups and few of disulphide bonds. No trace of tyrosine could be observed. The neurosecretory granules were associated with considerable amounts of cytoplasmic RNA. In general, stronger reactions were obtained in summer and winter than in other seasons.

The histochemistry of the neurosecretory material of the PF-positive neurosecretory cells of the cerebral ganglion of the adult and juvenile crab, Potamon magnum magnum (Pretzman) has been investigated. The PF-positive neurosecretory material is proteinaceous and contains considerable amounts of cystine; it is associated with significant amount of cytoplasmic RNA, lipids and phospholipids and with moderate amounts of carbohydrates, though no glycogen could be detected. The significance of these results is discussed.

The present study deals with acid and alkaline phosphatases activity determination in B cells of the thoracie ganglion of Potamon magnum magnum. Intense alkaline and acid phosphatases activity is seen in the neurosecretory granules as well as in the neural sheath. Acid phosphatase activity unlike alkaline phosphatase distribution, is seen in form of positive stained spherules showing different pattern of distribution. Alkaline phosphatase activity is linked with the metabolic process. The significance of these results is discussed.

Only four types of the secretory neurones were observed in the thoracic ganglion of the fresh water crab, Potamon magnum magnum (Pretzman). These cells are classified as A, A', B and C types. Our results also confirmed that the B and B' types of cells (BAID et al. 1968) are one and the same type, the B cells. The B cells are of two forms, with and without the axons. They clearly showed sequential histological patterns pointing out to their phases. The secretory material is discharged either through the periphery or through the axon and periphery both. The vacuoles were observed in both the forms of the B cells. The remarkable sign of the activity of the nuclear membrane especially at the beginning of the secretory cycle and the appearance of the first secretory granules around the nucleus strongly support the vital role of the nucleus in the initiation of the secretory cycle.

The epidermis of the fully mature earthworms, Dendrobaena atheca, has been investigated both histomorphologically and histochemically. The epidermis is constructed of two main cell categories: the glandular and nonglandular. The former comprises albumen, and small and large mucous cells whereas the latter includes supporting, basal and sensory cells. All these cell types rest on a prominent basement membrane and touch with their apices, except the basal cells, a thick layer of cuticle covering the epidermis. Epidermal cells are histomorphologically and/or histochemically distinguishable. Secretory granules of the albumen cells are proteinaceous in nature, those of the small mucous cells are neutral mucopolysaccharides and those of the large mucous cells are acid mucopolysaccharides. The histochemical nature of the cuticle indicates that it is mainly composed of neutral mucopolysaccharides and moieties of proteins and bound lipids.

The lateral-line system of the subadult and adult Neurergus crocatus crocatus Cope is retained throughout the life. It is constructed of pear-shaped sense organs or neuromasts which in the subadults are confined entirely to the epidermis with their apices opening distally to the exterior at the general level of the epidermal surface whereas in the adults they are embedded proximally more than halfway in the dermis with their distal apices opening into shallow grooves slightly below the regular epidermal surface. Dimensional differences are also observed between these organs in both stages. The neuromasts are constructed of 4 distinct cell types: sense cells, basal cells, sustentacular cells and mantle cells. These cells differ morphologically, structurally, topographically and functionally. The sense cells are clup-shaped, sensory, central in position and couched among the extremely elongated supporting basal and sustentacular cells, all of which are covered laterally by the extremely slender protective mantle cells. In both the mature and larvae, differences are observed among these cells in their size, number, location and arrangement. The sense organs are richly-supplied and well-nourished with vascular and nervous supplies.