Reactions of Molosoma to Chemical Stimuli 63 



are impinged upon by the chemical is evidentl) due to the forma- 

 tion of a protecting membrane or the thickening or hardening of 

 the mucus film which surrounds the body, under the stimulus of 

 the cold. 



d. The temperature is raised to about 20° C. The reactions 

 to these solutions are quic4:, almost violent. When the chemical 

 is applied directly in front of the prostomium the reaction invari- 

 ably brings about a complete reversal of the line of movement. 

 When applied laterally to the prostomium the reaction is directly 

 away from the pipette without preliminary testing movement. 

 When applied to the middle segments of the body the contraction 

 is so vigorous that in many cases oil globules and gland cells are 

 squeezed out in the process. In the case of the alkalies there was 

 noticed the beautifully rich magenta coloring observed by Bed- 

 dard ('89). Application at the posterior papilhe readily stimu- 

 lated the forward crawling movement even to "looping." 



e. The animals were subjected to very bright daylight for 

 several hours. 



With the water at a temperature of io°C. manyof the reactions 

 were in accord with the original experiments at 15° C. With the 

 temperature maintained at 15° C. the reactions were much more 

 vigorous and largely resembled those expressed in response to the 

 stronger solutions. Many of the contractions were vigorous 

 enough to squeeze out oil globules and mucus cells. With the 

 temperature raised to 20° C. the reactions were vigorous and 

 exhaustive, and in many cases proved fatal. 



The "Strong'' Stimuli 



Reactions Under Uniform Conditions 



Mineral Acids. When stimulated at the tip of the prostomium 

 there is a quick negative reaction which may reverse the direction 

 of movement. Sometimes the head is thrown only part way 

 toward the rear and the animal moves away at an angle. The 

 progress of the stimulus can be noted. The prostomium is first 

 bowed away from the stimulus; all the setse are erected rigidl at 



