Literary Notices. 167 



anterior end and oral groove earlier than with any other part of the 

 body. These are, moreover, the most sensitive parts of the body. 

 Now when Paramecium thus encounters a stimulating agent, it ap- 

 pears that these are the parts of the body that react. The animal at 

 first swims backward, circling at the same time toward the aboral side. 

 After a moment the animal swims forward again, still turning toward 

 the aboral side. The direction of its course is thus changed, and the 

 animal continues in this new direction if it does not again encounter 

 the stimulating agent ; but if it does, it goes through the same motor 

 reaction again, by swimming backward, turning toward the aboral 

 side and then swimming forward once more. This process is repeated 

 until the animal is finally brought beyond the range of the stimulus. 

 The animal invariably turns toward the aboral side, even when this at 

 first brings it more immediately into the region of the stimulus than it 

 had been before. The author aptly names this, orientation by trial 

 and error. And he further finds that this is the only manner of orien- 

 tation observable in Paramecia, and that this fact is utterly at variance 

 with the current theories of thermotaxis. 



The conclusions are based on extended observations of Parame- 

 cium, and they are confirmed by entirely concordant observations of 

 the other ciliate infusoria, Oxytricha fallax, O. aeruginosa, Stylonychia 

 myiilus, Stentor caendcus, Spuvstomum ambigiium and Bursaria triinca- 

 tella. Both heat and cold were tried as stimuli in nearly all the cases. 



Second Paper. Reactions to Light in Ciliate Flagellates. 



The reaction of the ciliate, Stentor, to light is the same as its re- 

 tion to heat and cold. It stops or swims backward a short distance, 

 then turns toward the aboral side, and resumes its forward motion. 

 "This is the reaction which is produced by strong mechanical stimuli, 

 by heat, and by chemical stimuli, acting upon the anterior end or 

 upon the body as a whole." And here too, the reaction is the same, 

 although at first the animal may be brought directly into the stimulus 

 which it is seeking to avoid. "-The direction of turning is thus deter- 

 mined by aji interfial factor — the structure of the body." The orienta- 

 tion is not governed by the direction of the light-rays (contra Loeb), 

 nor yet by the part of the body that receives the stimulation (contra 

 Verworn and others). Indeed the response is not altered if the 

 stimulus acts on all parts of the body at once. 



The flagellates normally swim in a spiral path, continually swerv- 

 ing toward that side which bears the larger "lip" and the eye, the so- 

 called dorsal side. While swimming toward a source of light Euglena 

 viridis will, if suddenly the illumination is decreased or greatly in- 



