1. Octopuses from which the vertical or median superior frontal lobes had been removed were able to discriminate between objects shown simultaneously, although they could not distinguish them when shown successively.
2. Discrimination by operated animals was however always less accurate than by controls.
3. A very difficult simultaneous discrimination could not be performed without the vertical lobes (although the same animal was able to make it before operation).
4. A discrimination learned by the simultaneous method before operation continues to appear (though less accurately) after vertical lobe removal.
5. The experiments therefore confirm previous evidence that the representations that ensure correct visual responses do not lie mainly in the vertical lobes, but else-where (probably in the optic lobes).
6. The function of the vertical lobes is considered to be to stabilize and perhaps lower the level of tendency to attack.