P.170 - §8 3. Gravity-explosion Planets. When a sun is born of a spiral or of a barred nebula, not infrequently it is thrown out a considerable distance. Such a sun is highly gaseous, and subsequently, after it has somewhat cooled and condensed, it may chance to swing near some enormous mass of matter, a gigantic sun or a dark island of space. Such an approach may not be near enough to result in collision but still near enough to allow the gravity pull of the greater body to start tidal convulsions in the lesser, thus initiating a series of tidal upheavals which occur simultaneously on opposite sides of the convulsed sun. At their height
P.171 - §0 these explosive eruptions produce a series of varying-sized aggregations of matter which may be projected beyond the gravity-reclamation zone of the erupting sun, thus becoming stabilized in orbits of their own around one of the two bodies concerned in this episode. Later on the larger collections of matter unite and gradually draw the smaller bodies to themselves. In this way many of the solid planets of the lesser systems are brought into existence. Your own solar system had just such an origin.

P.170 - §1 Not all spiral nebulae are engaged in sun making. Some have retained control of many of their segregated stellar offspring, and their spiral appearance is occasioned by the fact that their suns pass out of the nebular arm in close formation but return by diverse routes, thus making it easy to observe them at one point but more difficult to see them when widely scattered on their different returning routes farther out and away from the arm of the nebula. There are not many sun-forming nebulae active in Orvonton at the present time, though Andromeda, which is outside the inhabited superuniverse, is very active. This far-distant nebula is visible to the naked eye, and when you view it, pause to consider that the light you behold left those distant suns almost one million years ago.

  What is meant by "nebula" above is nebulous, to say the least.

When the book was written in the thirties, nebula and galaxy were not well defined, and the UB seems to have adopted the then current confused definition of nebula, when the authors meant "galaxy." It appears that nebula in the correct sense of galaxy has since fallen out of use.

The phrase "a spiral or a barred nebula" clearly indicates that the author meant 'a spiral or barred galaxy' in this case.