426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



able for being apparently effortless — and for most of its time the 

 bird does much more than that. It is so made that it must always 

 do something, even if it has nothing special to do, and quite a lot of 

 its behavior may be simply filling in time between one functionally 

 directed act and the next. The unceasing flow of energy must be 

 patterned and organized ; not every element in the design need in itself 

 be utilitarian. 



I venture the opinion that we should diagrammatize the driving 

 forces behind animal behavior, not so much in terms of the familiar 

 tank in which water collects at ever-increasing pressure until it escapes 

 through a spring-guarded outlet, as of a complicated system that can 

 never rest but has to oscillate in one or another of a number of pre- 

 determined alternative rhythms. This approach might help our 

 understanding of many phenomena, such as the appearance of "dis- 

 placement activities" when a straightforward course of action is 

 checked for one reason or another. It would indeed be surprising if 

 the thwarted animal did absolutely nothing at all. 



Ill 



What we have learned from worms and birds is true of many other 

 kinds of organisms too. More and more instances are appearing in 

 the literature of the importance of inherent rhythms in behavior. 

 The rhythms vary greatly in tempo and complexity. The organisms 

 in which they have been demonstrated include sea anemones, bivalves, 

 insects, sea squirts, sticklebacks, rats, and medical students — to men- 

 tion only a few. The work on mammals is mainly concerned with 

 long-period rhythms, correlated, for example, with the hunger con- 

 tractions of the stomach or with oestrus; shorter rhythms would be 

 harder to record automatically, and it is worth remembering that 

 mammals have characteristic voice rhythms as have birds. So, of 

 course, have many other animals, such as frogs and fishes, grass- 

 hoppers and cicadas. I thought it better in this lecture not to attempt 

 a catalog of examples, but to make my point by concentrating on two 

 contrasted groups. They are certainly not exceptional in basing their 

 behavior to a large extent on inherent and often arbitrary timing 

 mechanisms. 



And now a word in praise of worms. For obvious reasons, spon- 

 taneous behavior is most easily studied in animals that live under 

 sheltered and uniform conditions. The sense organs of my worms are 

 comparatively simple, and their way of living in burrows or tubes re- 

 stricts the number of disturbing stimuli which impinge on them from 

 without. Moreover, their activities are easy to record by the water- 

 current method, and they often show surprisingly normal behavior 

 patterns after drastic surgical operations — decapitation for ex- 



