1 Most ofthe fibers in the neuropil are unmyelinated, and myelinated fibers are scarce.

2 The present study have observed the fine structure of the neuroglial and neuronal processes of the hippocampal neuropil in the rats by using the technique of electron microscopy.

3 The axons and even the dendrites were dilated extremely to form irregular "balloon" which contained different vacuoles in size and distorted the structure of neuropil.

4 R_(7a) approximate many features of R_(1-6) cells, which have a larger, cell body, rhabdomere and axon, terminate in the first optic neuropil (lamina).

5 The results show that 5-HT immunoreactive processes originate from a relatively small number of cell bodies but each neuron has processes over a large volume of the neuropil of the brain.

6 Growth cones and myelinated fibers can be seen in neuropil.