The pioneering nature of Ricketts' book may be appreciated by comparison with another classic work, now in its fourth edition, that was published two years later, in 1941: "Light's Manual", by S. F. Light, of the University of California, Berkeley. "Light's Manual" is technical, difficult for laymen, but essential for specialists. On the other hand, Ricketts' "Between Pacific Tides" is readable, full of observations and side comments, and readily accessible to anyone with a genuine interest in seashore life. It cannot serve as a thorough manual to marine invertebrates, but it addresses the common and conspicuous animals in a style that invites and educates newcomers and offers substantial information for experienced biologists. It is not organized according to taxonomic classification, but instead by habitat. Thus, crabs are not all treated in the same chapter; crabs of the rocky shore, high in the intertidal, are in a separate section from crabs of lower intertidal zones or sandy beaches.