636 LIFE : OUTLINES OF GENERAL BIOLOGY 



tion of tentativ^e and spontaneity, as is well illustrated by the account 

 given by Jennings of the Amoeba's behaviour in pursuit of a smaller 

 one. The larger individual A, followed the smaller a, overtook it 

 and engulfed it. But a escaped through a weak spot in its pursuer's 

 protoplasm and glided away. Whereupon A turned on its course, 

 and caught a for the second time. A second escape followed, and no 

 recapture was effected. In cases like this there is a purposiveness 

 in the behaviour which cannot be described in purely physiological 

 terms. Even in the simplest forms of behaviour there is an indica- 

 tion that the organism is MiND-body as well as BoDV-mind. When 

 one watches a common Infusorian threading its way among the tangle 

 of Algoid filaments and the like under the microscope, one may 

 hesitate to use a word like "exploring", but is it possible to be 

 satisfied with "irritability"? The Infusorian is in part reacting, 

 like a dog hunting amidst the brushwood, to the diverse stimuli of 

 its environment, but it is at the same time obeying the fundamental 

 urge of hunger and self-assertiveness. If it were the size of a shark, 

 and we were bathing in its vicinity, would we doubt its purposiveness ? 



GENERAL VIEW.— Our survey suggests that there are two 

 main trends of behaviour: on the one hand, experimenting, initia- 

 tives, tentatives; on the other hand, answering back from an inborn 

 or acquired repertory of reaction-capacities. Both modes of be- 

 haviour have their advantages and disadvantages; the perfecting 

 of the second often makes an advance of the first more feasible, yet 

 the very perfection of the instinctiv^e may remove the spur to 

 intelligence. 



Beginning at the base, there are on the initiative side "trial and 

 error" methods, pre-intelligent efforts, tentative experiments, 

 associative learning, intelligent behaviour, and, in man, rational 

 activities. Similarly, beginning at the base, there are on the en- 

 registered side established reactions, reflexes, tropisms, rhythms, 

 instinctive behaviour, pre-intelHgent enregistration, habituation of 

 intelligent actions, and subconscious cerebration. 



Fig. 92 is an attempt to express the fact that the various 

 forms of animal behaviour are on different levels of complexity; but 

 it has, perhaps, the disadvantage of suggesting at first glance that 

 instinctive behaviour, for instance, leads on to intelligent behaviour, 

 whereas we hold that these two common modes of behaviour are on 

 different lines of evolution. We have sought to get over the difficulty 

 by using many separate branches. 



Behind the diagram there is a twofold theory: (i) that as we 

 a.scend the series of animal activities it becomes increasingly possible 

 and necessary to recognise a mental or psychical side, indicated by 

 the dotted line on the concavity of the curve, the physiological 

 accompaniment being indicated by the continuous convex lines; 



