BEHAVIOR 21 



''decide" to go in search for food. However, the case-bearing 

 roeseli would not abandon its home by mechanical shocks alone 

 even though Jennings struck it with a glass needle for an hour. 



Normal reactions of avoidance were also shown by stentors after 

 their " heads " had been excised (Jennings and Jamieson, 1902). 

 But stentors never became accustomed to truly injurious stimuli 

 such as salt solutions (see also Merton, 1935) or sharp poking, 

 though they learned to put up with a lot of minor disturbance. 

 This may happen frequently in nature and stentors growing among 

 Tuhifex have been observed to continue feeding and not contract 

 though constantly struck by the worms. Jennings provided a simple 

 demonstration of this accommodation by attempted equal impacts 

 with a glass needle repeated each time after re-extension of the 

 stentor. After about a dozen strokes there was no contraction 

 response unless the animal was poked several times. The longer 

 this was continued the greater w^as the number of strikes which 

 were necessary to elicit contraction, although there was some 

 irregularity probably due to inequality of impacts. Eventually the 

 animals detached and swam away. Sometimes there was a ready 

 response only at first, repeated proddings then eliciting no response 

 until the animals swam away. But in these cases he noted that the 

 stentors did not remain oblivious to the blows but twisted continu- 

 ally and turned away as if to avoid them, finally detaching and 

 swimming away. Hence in accommodation there was a reversal 

 of the sequence of avoiding reactions, for example, contraction 

 later replaced by merely turning away. Similar abolishment of 

 major avoiding reactions occurred in other contractile ciliates 

 {Epistylis, Vorticella, and Carchesium) and was noted by Holmes 

 (1907) in Loxophyllum. 



This orderly change in response was not due to reaction fatigue. 

 About a minute was required for re-extension and this should have 

 been sufficient for complete recovery. Also, stentors could be kept 

 continuously contracting for an hour at a time, but they very soon 

 ceased responding to weaker stimuli. Nor could the response have 

 been due to sensory fatigue because the animals showed continued 

 appreciation of the stimulus (by turning away) and because stentors 

 subjected to strong mechanical blows or injurious salt solutions 

 continued reacting indefinitely. Schaeffer (1910), for instance, said 

 that coeruleus would swim backward, without spiralling, continu- 



