LIGHT AND MOVEMENT 31 



Romanes. Animal Intelligence, X.Y. Verworn. Psychophysiologische Protisten- 

 (1883). studien, Jena (U 



Russell. The Behaviour of Animals, 2nd. Volta. Galvanismus u. Entdeckung d. 



Ed., London (1938). Sdulenapparates (1796-1800). 



Sachs. Vorlesungen iiber Pflanzen physio- Willis. De motu animalium, London 



Zo^/c, Leipzig (1882). (1670). 



The Types of Motorial Responses 



The behavioural responses of organisms to hght are diverse and for 

 three-quarters of a century workers in this field have made numerous 

 attempts to rationalize them into a single system of classification. 

 While terminology itself cannot claim to be an end of science — and, 

 indeed, its apparent definiteness is often misleading — the labelling 

 and classification of phenomena are of great value in the economy and 

 clarification of thinking. Adequate classification, however, entails 

 fundamental knowledge and it is not surprising in a subject which is 

 still highly controversial and inadequately understood that agreement 

 has not yet been reached. 



In this connection several terms have been introduced into the literature. 

 Strasburger (1878) in his revolutionary work on botany, wherein he made a 

 fundamental study of the movements of plants, used the term phototropism 

 ((f)U)s, (fxjoTos, hght ; TpoTirj, a turning) to describe the mov^ements of sedentary 

 plants in contradistinction to phototaxis (rants', a precise arrangement) to 

 describe the locomotor reactions of freely moving organisms to light. Shortly 

 thereafter, Engelmann (1883) introduced the term kinesis (/ctvi^at?, a movement) 

 to indicate reactions wherein the \-elocity of movement depended on the strength 

 of the stimulus. The next contribution to terminology was due to Pfeffer 

 (1904) who introduced the useful differentiation of phobotaxis (^o'jSo?. fear) to 

 describe random, trial-and-error avoiding naovements, and topotaxis (totto?, a 

 place) to indicate directional attraction movements, while Kiihn (1919-32) 

 subdivided the latter into four categories of increasing complexity in responso, 

 which we shall adopt — tropotaxis, telotaxis, menotaxis, and mnemotaxis.^ 

 To these, Gunn and his colleagues (1937) added the term kxinokinesis and 

 klinotaxis {kX'lv oj, bend) to express changes in orientation determined by 

 turning movements. The term scototaxis {aKoro?, dark) suggested by Alverdes 

 (1930) and Dietrich (1931) is probably unnecessary since those movements 

 which may be interpreted as the result of an attraction to darkness are probably 

 best looked upon as a negative phototaxis. 



It is true that against this urge for classification some have rebelled (Mast, 

 1938), but although the dangers of a system of classification in concealing 

 ignorance are obvious, its advantages are so considerable that as a tentative 

 measure we will base oiu" terminology on the classical scheme of Kiihn, introduc- 

 ing some modifications advanced by Fraenkel and Gvmn (1940). It is to be 

 remembered, however, that the tj^^es of response are by no means mutually 

 exclusive and that in their activities many animals show a combination of 

 reactions. 



A somewhat revolutionary view has recently been advanced by 

 Viaud (1948). He divided the reactions of animals to light into two 

 types : 



1 p. 43. 



