CHAPTER VI 

 BEHAVIOUR 



Behaviour can be denned in its widest sense as any change in 

 activity made by the intact animal. This rules out the responses of 

 isolated parts in physiological preparations, though such prepara- 

 tions can play a part in the analysis of behaviour. However, 

 behaviour is fundamentally a characteristic of the whole animal, 

 and is usually more than the sum of its physiological mechanisms. 

 The additional ' something ' is gained by the integration and co- 

 ordination, often coupled with mutual inhibitions, of these 

 mechanisms to form the complicated mechanism of the whole 

 animal. 



Our definition has been made purposely wide so that almost any 

 change of activity can be included. Even the adoption of a posture 

 is an active process involving reactions to various features of the 

 environment. A change of posture is clearly a part of behaviour. 



Before we deal with complicated behaviour patterns it will be 

 as well to try to find out the extent to which a crustacean is aware 

 of its environment. How much can it see? Can it hear, or feel, or 

 smell? These questions can be answered with varying degrees of 

 completeness, and the answers depend on how much we know 

 about the structure and functioning of the various sense organs 

 which the Crustacea possess. 



The most conspicuous of these organs are the eyes. In a typical 

 decapod each eye consists of several hundred tubular units radiating 

 from the end of the optic nerve. Each of these units is a miniature 

 eye (fig. 39). There is a central optical tract, with a crystalline cone 

 and a crystalline tract at its base leading to a group of cells known 

 as the retinulae. Sometimes the crystalline cone abuts directly on 

 the retinulae, without any intervening crystalline tract. Each 

 tubular element is isolated from the others, to a greater or lesser 

 extent, by two groups of pigment cells; one group (distal) around 

 the crystalline cone, the other group (proximal) is arranged around 

 the retinulae. Both groups of pigment cells can cause their dark 

 pigments to move and cover varying amounts of the tubular eve. 



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