22 THE BIOLOGY OF STENTOR 



ously for three hours in a dish of dense carmine particles. Therefore 

 if learning be altered response due to previous experience, this did 

 in fact occur. 



The weaker the stimulus the more rapid the accommodation. 

 To a jet of water from a capillary pipette coeruleus responded only 

 once by contraction and thereafter merely bent in a new position. 



If stimulated while swimming, Jennings (1899) reported that 

 polymorphus contracts and backs up a short distance then turns to 

 the right side always and swims off in another direction. This 

 response was invariable, regardless of the point of stimulation. 

 Though the posterior end was less sensitive than other parts, a 

 sharp blow here elicited the same response, which therefore 

 carried the animal toward rather than away from the point of 

 stimulation. Unlocalized stimulation such as jarring the dish also 

 evoked the same avoiding response, as did diffuse chemical 

 stimuli. 



Unlike Paramecium and Chilomonas, stentors were completely 

 indifferent to bubbles of carbon dioxide or solutions of acids, not 

 showing the spontaneous aggregations of the former (Jennings 

 and Moore, 1901-02). 



Even to relatively strong solutions of cane sugar roeseli showed 

 no avoiding reaction and responded by sudden contraction only 

 after the cell became obviously affected by osmotic pressure 

 (Jennings, 1902). 



4. Response to light 



Jennings (1902) noted that roeseli does not respond to light of 

 ordinary intensities. According to Schulze (1951) polymorphus 

 shows contrasting reactions to hght depending on whether sym- 

 biotic Chlorella are present: green animals appropriately went to 

 the lighted side of the aquarium but white forms collected on the 

 dark side. Hammerling (1946) stated th^t polymorphus is sensitive 

 to strong light and that cultures had to be screened, but in nature 

 I have found these stentors fully exposed to brightest summer 

 sunshine. In coeruleus the reaction seems to vary with the strain. 

 Testing 8 races cultured in the same manner, fed on the same 

 day each week, and producing animals of about the same intensity 

 of green pigmentation, I found that two showed a strong negative 

 response to daylight and quickly accumulated on the side of the 



