1. The distribution and termination of nerve fibers in the mammalian and avian adrenal cortices was histologically investigated in sections treated with a modification of the Bielschowsky silver-impregnation method.2. Juxtacapsular ganglia were found in the monkey and dog. In the capsule of the adrenal gland, nerve cells were observed singly or in small groups. Scattered nerve cells were occasionally found in the zona fasiculata and the zona reticularis, too.3. In the capsule, many terminal formations of afferent nerve fibers were observed in the dog.4. Fine strands of the autonomic endformation made plexuses around the nests of cortical cells in all the cortical zones.5. Probably afferent nerve fibers were recognized to terminate in the cortical zones.6. The blood vessels in the cortex were innervated by probably afferent as well as efferent nerve fibers.7. In the adrenal gland of the fowl, fine nerve fibers were recognized to be distributed to the nests of cortical cells as well as to the blood vessels. Larger blood vessels were probably supplied with afferent fibers. Besides, complicated receptor formations were observed among the cortical cells.