An electron-microscopic study was carried
out on the median eminence of cats during post-natal
development. From the moment of birth (observations
performed 12 hours later) Herring bodies were seen in
the fibrillary layer of the median eminence. At 45 days
after birth, myelinated nerve fibres could be observed,
some of them containing neurosecretory granules. The
number of myelinated fibres in the median eminence
increased with age and at 90 days some Herring bodies
appeared surrounded by myelin sheaths; these mainly
contained neurosecretory granules and a few mitochondria