The distribution and cytoarchitectonic pattern of the magno- and parvocellular hypothalamic nuclei of the cobra,Naja naja, are described at the light-microscopic level. With respect to their tinctorial affinity to paraldehyde fuchsin (AF) as a representative of the Gomori-type of stains, the magnocellular neurons belong to the “AF-positive” and the parvocellular neurons to the “AF-negative” elements. In addition to the supraoptic and paraventricular nuclei proper, two accessory aggregations of magnocellular neurons, thenucleus retrochiasmaticusandnucleus circularis, can be identified. Although in a peculiar location, they may be regarded as subunits of the supraopticoparaventricular neurosecretory complex. As many as 22 “AF-negative” nuclear areas are identified in the hypothalamus of the cobra. Thenucleus periventricularis hypothalamiof earlier authors is subdivided into several circumscribed neuronal complexes. Thenucleus arcuatus,nucleus hypothalamicus lateralisandnucleus lateralis recessus infundibuliare well developed. An attempt is made to interpret the significance of these nuclei on a comparative and phyloge
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