Asymmetry of the habenulae in the elasmobranch "Scyllium stellare". II. Electron microscopy.

The structure of the habenular nuclei of the elasmobranch Scyllium stellare has been examined with the electron microscope. There is asymmetry of the left and right habenulae; difference is manifest in their cell types and myelin distribution. The presence in only the left habenula of cells bearing large granules - probably secretory - and of cells with myelinated perikarya suggest a functional diversification of the habenulae. A large variety of synaptic vesicles occur in the habenulae of both sides but we could not demonstrate a preferential localization of one particular type in specific habenular subnuclei. A feature common to all portions of the habenular complex is the presence of multilamellar astroglial formations wrapping cell bodies and synapses.