PROBLEM I. The Shnplest Forjns of 



vations we know that much of what 

 seems, at first glance, to be intelHgent 

 behavior in lower animals requires no 

 intelligence. 



The misuse of words. Some technical 

 terms used by scientists and defined in 

 this book are often used carelessly in 

 everyday speech. In the biology class- 

 room you must learn to use exactly the 

 words so frequently misused in ordinary 

 conversation. For example, people may 

 say, "He mstinctively defended the good 

 name of his high school." Now you 

 know that the action was not an instinct, 

 as instinct is defined above. The action 

 was not inborn. When a skillful automo- 

 bile driver makes a quick move that pre- 

 vents an accident, some people say, "His 

 reflexes are wonderful." Of course, it is 

 not his reflexes that are wonderful, for 

 the skilled driver was not born with the 

 ability to drive his car. In a later problem 

 we will read why and how he avoided 

 an accident. 



Behavior in the simplest animals. The 

 simple response to a stimulus described 

 in you and other animals occurs in pro- 

 tozoa, too. Professor H. S. Jennings, who 

 spent many hours studying the behavior 

 of protozoa and other simple forms, re- 

 lates how he once watched a large ameba 

 pursue a smaller one back and forth 

 across the slide. After a long chase the 

 pursuer began to pinch off a small piece 

 of its prey (see A in Fig. 251). It suc- 

 ceeded in pinching off the piece and be- 

 gan to engulf it as it would engulf any 

 particle of food (see B of Fig. 251). 

 But the small piece of ameba was alive 

 and active, and by sending out pseudo- 

 pods, it flowed away from its captor 

 (see C of Fig. 251). Again it was chased 



Behavior in Anmicth 



26s 



and engulfed. Again it escaped. This 

 time the large ameba stopped chasing 

 the smaller one. But do not think that it 

 gave up "in despair" for, as far as we 

 know, neither the large ameba nor the 

 small one was in any way conscious of 

 what it was doing. The small ameba was 

 not "afraid" of its pursuer, nor did it 

 "try" to escape or plan its actions. The 

 behavior of both amebae was typical of 

 that of any protozoan at all times. The 

 small ameba was a food stimulus to the 

 larger one; the larger one responded by 

 sending out pseudopods in the direction 

 of the stimulus. The small ameba was 

 also responding to a stimulus; its response 

 was the forming of pseudopods in the 

 opposite direction. Both were perform- 

 ing reflex acts. Neither showed intelli- 

 gence any more than the spider in 

 building its web, or the bush turkey in 

 wriggling out into the open. You can 

 study reflexes in protozoa by doing Ex- 

 ercises 4, 5, and 6. 



Fig. 251 Responses in two a?f?el?ae. Is this be- 

 havior i?itellige?it or reflex? 



