ANIMAL BEHAVIOR — WELLS 417 



spreads through the body can be controlled to some degree. The gen- 

 eral situation is roughly parallel to that of a vertebrate heart. The 

 isolated heart will continue to beat and so will little shreds of heart 

 muscle, but in the body its activity is modified by regulating nerves. 

 So also with the lugworm esophagus ; it has an inherent rhythm which 

 can be regulated; but its pattern, being intermittent, is more com- 

 plicated, and in this case the pattern can spread through the body and 

 cause periodic movements of the whole animal. 



These facts impressed me, when I first came across them, for the 

 following reason. When I was a young man I was a mechanist of the 

 most bone-headed type — believing that behavior was nothing more 

 than a series of reflexes. The animal was stimulated by the presence 

 of food, or an enemy, or a mate, or by some simple organic need, and 

 it performed appropriate deeds. If it happened to be a very intelligent 

 animal — as a man is, or an octopus — it could form conditioned re- 

 flexes, and then its reactions were more complicated. But always it 

 was driven, and its life was patterned, by the incidence of stimuli of 

 one kind or another. Presumably, as a corollary, a physiologically 

 satisfied animal in a homogeneous environment would do nothing at 

 all ; but I do not remember that I worried very much about that. I 

 think that if one did not know what it was that stimulated a par- 

 ticular act, one called it a drive. Be that as it may, in the lugworm 

 we see something rather different. The characteristic activity pattern 

 of the isolated esophagus is part of its organization — if you like, part 

 of its structure. The rhythmic outbursts begin spontaneously, with- 

 out any external stimulus or any biological need ; they subside without 

 any kind of satisfaction; and normally their rhythm plays an im- 

 portant part in patterning the life of the worm as a whole. 3 



3 The basing of the lugworm's behavior on inherent rhythms, instead of on 

 simple responses to its immediate needs as they arise, has definite survival value. 

 The flat beaches frequented by these worms are often covered with puddles and 

 sheets of water at low tide. On a sunny day this water may be several degrees 

 hotter than the underlying sand, and well above the highest temperatures which 

 the worms can tolerate. A sharp frost or a heavy downpour of rain could also 

 make the surface water harmful to the worms. Normally, the worm drives water 

 through its burrow to get a supply of oxygen; if the surface water became 

 dangerously hot or dilute a reflex hyperpnoea in response to oxygen lack might 

 be disastrous ; it would be wiser for the worm to suspend its activities. When 

 placed in a glass tube under unfavorable chemical conditions the worm becomes 

 relatively inactive; but under the influence of its 40-minute rhythm it makes 

 periodic backward trips toward the top of the tube and generally draws a little 

 water along on these occasions, as if testing the surface water. We may guess 

 that when unfavorable conditions develop in the field, it behaves in the same 

 way; after the rising tide has covered the burrow again and so removed the 

 danger, the fact will be detected at the next testing excursion, and the worm's full 

 activities will then be resumed. 



