1. The detailed morphological structure of neurosecretory cells inLaevicaulis is given. There are two types of cells: cell type A is pyriform ranging from 83 to 133 µ in length, whereas cell type B is oval and is 49 to 66 µ in length. In both the cell types axonal transport of the secretory material is noticed. Both the cell types are PAS negative and positive for proteins and lipids.
2. Histological structure of the optic tentacle reveals that it consists of three types of neurosecretory cells of which the collar cells are situated around the central ganglia while the others are laterally down the sides of dermo-muscular wall. They are PAS positive and sudanophilic.
3. Cell type B showed a distinct annual cycle of activity which is correlated with the annual reproductive cycle ofLaevicaulis.
4. The effect of cutting the tentacles showed that number of eggs was increased in optic tentacles-cut animals. The tentacle homogenate injected animals showed no increase in number of eggs but the brain homogenate injected animals showed considerable increase in the number of eggs.
5. The amount of neurosecretory material in cell type A decreased from lower to higher salt concentrations. It may conclude that cell type A plays an important role in water balance as anti-diuretic factor.