THE ANALYSIS OF BEHAVIOUR IN ANIMALS 163 



to light is not influenced to the same extent by excess of Ca 

 and Mg. As a bionomic illustration of these phenomena 

 the following suggestion by Loeb is based on the fact that larvae 

 of Porthesia, which as already observed are strongly photo- 

 tropic, become indifferent to Hght after a meal. Porthesia 

 lays its eggs on a shrub. The larvae hatch out in autumn and 

 hibernate on the ground. Provided that the temperature is 

 raised sufficiently they can be induced to leave the nest at any 

 time. When they emerge of their own accord they crawl 

 directly up the shrubs on whose leaves they feed, always 

 moving upwards, i.e. in the direction of the rays reflected 

 from the sky. At the top of the shoot they encounter young 

 buds, where they feed, and becoming phototropically 

 indifferent in consequence, are free to move downwards and 

 thus ultimately find another source of food. 



Conditioned or Associative Behaviour.— The phenomena of 

 reflex action as studied in a mammal from which the cortex 

 has been removed are predictable, and there is reason to hope 

 that they will fall into line with the phenomena of peripheral 

 conduction, summation, and inhibition as suggested in the 

 last chapter. We have seen that considerable progress towards 

 a knowledge which will enable us to predict the behaviour 

 of intact animals has been made by (i) analysing the interaction 

 of reflex systems brought into play by different classes of 

 stimuli normally present in the surroundings, (2) determining 

 the way in which reflex responses may be modified by physico- 

 chemical factors in the external medium. There is, however, 

 a further aspect of response which has to be taken into account 

 in discussing the behaviour of animals. It can be illustrated 

 well enough by the feeding of minnows. If food in the form 

 of pieces of meat is presented to it the animal behaves in a 

 predictable way ; it snaps at the food. If paper coloured to 

 resemble pieces of meat is presented, for the first few times 

 the fish behaves in a predictable v/ay by snapping. After a 

 number of trials which can be predicted within limits by 

 experiment, the fish no longer snaps at the paper. To the 

 mechanism which conserves the effects of previous stimulation 

 psychologists still employ the subjective term '' memory." 



