Book Review Neurons and Networks: An introduction to neuroscience By John E. Dowling. 447 pp., illustrated. Cambridge, Mass., Belknap Press/Harvard University Press, 1992. $45. ISBN 0–674–60820–8 . An Introduction to Molecular Neurobiology Edited by Zach W. Hall. 555 pp., illustrated. Sunderland, Mass., Sinauer, 1992. $46.95. ISBN 0–87893–307–7 .