24 THE BIOLOGY OF STENTOR 



response varied directly with the temperature, and this may not be 

 solely due to increased rate of ciliary beating but also to the en- 

 hancement of photoreactions in the cell. 



Dabrowska (1956) was unable to get coeruleus to associate an 

 electric current with its response to light, and hence learning by 

 conditioned response was not demonstrated. 



5. Response to heat and electric current 



Alverdes (1922) found th^t polymorphus reacted to heat with a 

 typical avoiding response. This response disappeared when the 

 anterior end was cut off, for the cell body then swam indiscrimin- 

 ately towards the heated end of the slide and was killed. To a i % 

 solution of table salt the headless cell bodies gave the avoiding 

 response just as whole animals. He concluded that warmth percep- 

 tion is limited to the anterior end while chemical sensation is over 

 the entire body surface. This interpretation is open to question, 

 first, because salt apparently compels ciliary reversal with contin- 

 uous backward swimming by direct action on the coordinating 

 mechanism, and second, because as Dierks (1926b) pointed out, 

 the response of the isolated heads was not indicated. Anterior and 

 posterior half fragments would better have been compared since 

 both are capable of typical avoiding reactions, with use of a less 

 noxious chemical stimulant like carmine particles. 



With further regard to sensory localization, Roesle (1902) 

 claimed that the mouth is the part of stentor most sensitive to 

 electric currents but behavior of stentors with mouthparts excised 

 was apparently not studied for comparison. Roesle also reported 

 that an induction current stimulates Stentor to contraction only 

 when the direction of the current was parallel to the axis of the 

 animal, contrasting with muscle physiology in which stimulation 

 is independent of the orientation. Yet Hausmann (1927) found 

 that polymorphus contracted and backed up in an electric current 

 but without correlation with its direction. Stentor was more 

 sensitive than smaller ciliates of other genera so that at least the 

 intensity of the response may be correlated with body size if the 

 animals compared normally swim at the same speed. Dierks Roesle, 

 neuroid (1926b), repeating the electrical stimulation studies of 

 found that Stentor was more sensitive to the current than any of 

 the other cihates tested, which he credited to the presence of fibers. 



