two coiled arms radiating diametrically from a central nucleus and dilating outward. Even nebulæ not originally supposed spiral have disclosed on better revelation the dominant form. Thus the great nebula in Andromeda formerly thought lens-shaped proves to be

a huge spiral coiled in a plane not many degrees inclined to the plane of sight.

As should happen if the spirals are unrelated, left-handed and right-handed ones are about equally common. In Dr. Roberts' great collection of those in which the structure is distinctly discernible, nine are right-handed, ten left-handed, showing that they partake of the ambidextrous impartiality of space.

Lastly the spirals are evidently thicker near the