Conditioning, to a vibratory CS, of a withdrawal response elicited by a light US was studied in 2 groups of decerebrate earthworms. Imposition of a long delya in the apparatus before training did not affect the subsequent course of conditioning. The failure of worms to show CRs when trials are spaced was confirmed, and was explained in terms of the reduction in URs during spaced training. (PsycINFO Database Record (c) 2006 APA, all rights reserved)