418 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



At this point an obvious question arises. I have spoken of the 

 esophagus as a physiological alarm clock. How does the clock work ? 

 From what kind of cellular mechanisms does its regular intermittent 

 pattern arise? The first step in trying to find an answer is to pull 

 the clock to pieces. If you cut a lugworm esophagus into several bits, 

 cutting either lengthways or across, you find that each of them shows 

 the characteristic alteration of rhythmic activity and rest, from 

 which it seems that the pattern is a general property of the esophageal 

 wall. The fine structure of the wall was described by Dr. Whitear; it 

 contains a diffuse network of nerves which may be responsible, but 

 unfortunately the anatomical arrangement is not favorable to further 

 attempts at identifying the active structures. On the purely physio- 

 logical plane some light could perhaps be thrown on the nature of the 

 mechanism by varying the temperature and composition of the sur- 

 rounding fluid; and I have published some experiments along these 

 lines in collaboration with Miss Ledingham. But the essential prob- 

 lem remains unsolved. The esophagus can be slowed down by increas- 

 ing the amount of magnesium in the surrounding fluid, and it may then 

 show its outbursts of activity at very regular intervals of over half an 

 hour. The problem of how to construct a clock of cellular dimensions 

 that will tick as slowly as this is indeed an intriguing one. It is pre- 

 sumably related to many of the problems with which the physiologist is 

 concerned, such as the exact mechanism of the heartbeat. Under cer- 

 tain abnormal conditions a heart may beat in intermittent bursts, and 

 its activity pattern is then very like that of an isolated lugworm 

 esophagus. Perhaps when our physiologists have published all the 

 answers to their problems the results may be applied to mine. 



With that I shall leave the Arenicola esophagus and begin to broaden 

 the picture, but first a word must be said about one of the experimental 

 methods. We are going to consider the results you get, if you observe 

 the behavior of a polychaete continuously for days or weeks on end, 

 and this may sound a hard thing to do, particularly if the worm is 

 burrowing, invisible, in sand, or living (as is the way of many species) 

 in an opaque tube of its own construction. In practice, however, it is 

 easy to persuade the worms to write down on paper what they are 

 doing; and possible (although more difficult) to learn to read what 

 they write. It all depends on the fact that they drive water through 

 their tubes in order to get oxygen, and often for other reasons too. 

 The method consists of three stages : (a) you set up a simple apparatus 

 which traces on slowly moving smoked paper the speed and direction 

 of the water currents, so that you can see how the currents vary with 

 time; (b) you find, in many species at least, that certain characteristic 



