The type A neurosecretory cells of the pars intercerebralis in C. bifida have axons that pass direct to the region of the dorsal aorta. When insects are in their normal hyposmotic medium, these protocerebral NSC have moderate amounts of neurosecretory material. In isosmotic or hyperosmotic media there is a considerable reduction in stainable material, whereas when they are in distilled water, the protocerebral NSC stain deeply, the cells being loaded with neurosecretory material. The depletion of neurosecretory material under potential dehydration conditions strongly suggest that water balance in C. bifida is under neuroendocrine control. Comparison with the described conditions in other insects suggests that the protocerebral NSC in C. bifida produce an antidiuretic principle.