182 THE PHYSIOLOGY OF EARTHWORMS 



the performance of worms in a maze. This observation has been 

 expanded by Arbit (1957) in a similar series of experiments 

 carried out at 12-hour intervals. L. terrestris introduced into a T 

 maze between the hours of 8 a.m. and mid-day took longer to 

 acquire the habit of turning to the correct side than did worms 

 trained between 8 p.m. and midnight. The latter group also needed 

 less stimulation by touch or Hght to start them moving along the 

 maze. Earthworms are evidently more * 'alert" during the night 

 hours. 



Activity 



It is well known that earthworms come to the surface of the 

 ground during the hours of darkness and some wander freely about 

 feeding and mating. But anyone who has watched a bird on a 

 lawn will not doubt that many earthw^orms are also to be found at 

 the top of their burrow during the hours of daylight, even though 

 they are photonegative to high intensities of light. 



Studies have been made on the patterns of activity shown by 

 earthworms under conditions of dark or low illumination. Baldwin 

 (1917) watched earthworms and concluded that they were most 

 active between 6 p.m. and midnight and Szymanski (1918) found 

 that they were most active between 2 p.m. and midnight. More 

 recently Ralph (1957) used actographs, dishes supported on knife 

 edges, to provide a visual record of the motor activity of L. terrestris. 

 Theleastactivity was manifested between 7 and 11 a.m. with relatively 

 high rates of movement before and after these times, reaching a 

 peak in mid-afternoon and lasting through till early morning. This 

 activity cycle did not reflect the diurnal rh)1:hm of oxygen uptake, 

 but no attempt was made to explain what happened physiologically. 

 Harker (1960) has demonstrated a hormonally controlled "internal 

 clock" in the cockroach which may explain the diurnal variation in 

 the activity in this species. It is possible that in the earthworm there 

 is another example of the same phenomenon, although no evidence 

 is available. Neurosecretory cells, however, are present in the 

 earthworm and all their functions cannot yet be known so that the 

 postulation of an "internal clock" may not be completely fanciful. 



Siim?nary 



The appearance of complex behaviour patterns has been 



