CHAPTER IX 



THE ANALYSIS OF BEHAVIOUR IN ANIMALS 



In the last chapter the attempt has been made to indicate 

 some of the evidence available for an understanding of the 

 nature of the processes involved in the transmission of the 

 excited state. It will now be necessary to inquire into what 

 is known regarding the way in which stimuli normally present 

 in the surroundings operate to produce the characteristic 

 and more or less appropriate sequence of responses which 

 constitutes an animal's behaviour. It will coincide best 

 with our present treatment to consider the question from a 

 phyletic standpoint. 



The simplest form of response is the direct reaction of 

 an effector organ to external stimuli. This has been already 

 met with in the pigmentary effector organs of the shrimp 

 and lizard. The reaction of the iris to light in vertebrates 

 and cephalopods is another instance. But in both cases we 

 find a co-ordinating mechanism superimposed upon the local 

 form of reaction. In the osculum of the sponge with its collar 

 of primitive muscular elements we have an apparently purely 

 local mechanism. No co-ordinating arrangement is shown 

 by the behaviour of other oscula when a neighbouring one 

 is stimulated. Their normal function is to react to running 

 water by relaxation and to still water by closure, response 

 occurring after an interval of several minutes. 



Neuroid Transmission.— Undifferentiated protoplasm pos- 

 sesses the property of propagating the excited state. This 

 is best seen in the co-ordination of ciliary movement, so 

 important an aspect of behaviour in large numbers of marine 

 animals. Ciliary motion is metachronial ; the cilia do not 



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