Orienting reaction in invertebrates.

Changes in motor and vegetative indices in freshwater crayfish during sudden changes in the environmental situation are described. The results suggest that freshwater crayfish characterized by a sedentary lifestyle nevertheless constantly control the milieu in which they find themselves, by recording diverse changes in its parameters. Apparently the physiological nature of the reactions to "neutral" stimuli issuing from the milieu, is, in representatives of the higher invertebrates, very similar to that of the higher mammals, and may be described using the concepts of the orienting reflex and activity of an investigatory character which follows it. The question is posed in this context of the possibility of the appearance in this situation of emotional reactions of the animals investigated.