A distinction must be made between primary and secondary spirals. Primary spirals arise early in life and have firm outlines; they are the great majority of spirals. Secondary spirals tend to be ghost-like; they certainly overlap normal and possibly also the primary spirals. Before breeding data became available (appendix 4), it was believed that primary spiralization was not an all-or-none charac- ter, but rather one limb of a U-shaped distribution with a small contingent of intergrades between axial and spiral phenotypes. It now appears more likely that basically axial and primary spiral patterns are distinct entities, and that the 'intermediates' are in fact secondary spirals which become manifest under certain conditions