Errol E. Harris, The Foundations of Metaphysics in Science, Londres, Allen and Unwin, 1965, p. 235.
Work of building and provisining the nest and to vary their methods of construction in order to men holeds which he had artificially made in the nest . And finally he describes the elaborate and versatile methods of tube building of the caddis larva (Molanna) as revealed by the work of Dembrowski and used by Russell as one of the outstanding examples of variably directed activity.
Secondly, the occurrence of a sign-stimulus does not necessarily determine which of a number of alternative mechanism will be brought into play in this discharge..