The Sources of Animal Behavior 1 



By G. P. Wells 



Professor of Zoology- 

 University of London 



For nearly 20 years now I have worked on various aspects of the 

 biology of a group of marine worms — the polychaetes — mainly, though 

 not exclusively, on the members of one family. An intensive study of 

 that kind has its own fascination, and it becomes particularly reward- 

 ing if the investigator is lucky enough to find that his animals illus- 

 trate with exceptional clarity some principle of wide application in 

 biology. I believe this can be said of the behavior of my worms, and 

 although the belief may be merely the rosy illusion of a specialist (for 

 I tend to see any biological problem in worm's-eye view) , I shall try 

 to develop the theme here. I shall start with the only species I know 

 at all intimately — the common European lugworm, Arenicola marina, 

 and go on to certain related species and then to quite different kinds of 

 animals. My aim is to show that even a worm may have a useful con- 

 tribution to make to our understanding of animal behavior in general. 



The lugworm is commonly about the size of a fountain pen — though 

 it may be rather larger, or very much smaller. It is found at low tide 

 by digging in beaches of muddy sand. It lives in a fairly permanent 

 burrow, eating the sand, digesting some of the organic content, and 

 ejecting the unwanted residue on the surface. These residues collect 

 as a heap of sandy cylinders; most of us have walked across a flat 

 beach when the tide is out, and seen the little heaps in their thousands. 



The lugworm's brain is very small and its nervous system is com- 

 paratively simple ; it leads an extremely sheltered life, surrounded by 

 the sand, which is at once its food and its protection from the hazards 

 of the world : and one might reasonably expect, from these facts, to 

 find that its behavior consists largely of simple responses to stimuli, 

 most of which come from within. For example, one might expect it 



1 Inaugural lecture delivered at University College, London, May 5, 1955. Re- 

 printed by permission. 



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