sentences:  Indeed, later experiments showed that in both invertebrate and vertebrate models, axons grew along pre-determined routes to create a reproducible scaffold of nerves.Ramon y Cajal's views faced some competition from those of Paul Alfred Weiss, his contemporary neuroscientist during the 1920s and 1930s.Weiss argued that functional specificity did not depend on specific axon connections, and that nonspecific mechanical cues participated in guiding axons.