NEUROSECRETORY CELL TYPES AND THEIR SECRETORY ACTIVITY IN THE CRAYFISH ,

Abstract

1. There are four cytologically distinct types of neurosecretory cells in the eyestalk and brain of Orconectes virilis. Two of these neurosecretory cell types are restricted in their distribution to the x-organ. The other two cell types occur in all neurosecretory cell groups in the eyestalk and brain except the x-organ. 2. The distribution of neurosecretory cell types has been compared with that described by Enami (1951) for Sesarma. 3. The Type 2 neurosecretory cells are the only neurosecretory cells that undergo histologically demonstrable changes in secretory activity in relation to the molting cycle. It is suggested, therefore, that the Type 2 neurosecretory cells are the source of the molt-inhibiting hormone. 4. Arguments are presented in favor of the view that at some time before molt a decrease occurs in the rate of release of molt-inhibiting hormone from the axon endings of the Type 2 neurosecretory cells. This decrease seems to be correlated with a concurrent accumulation of stainable material observed in Type 2 neurosecretory cell bodies.