200 



BEHAVIOR OF THE LOWER ORGANISMS 



the same reaction has the opposite effect, subjecting the animal still 

 further to the action of the stimulating agent; other reactions must 

 supervene before the animal is removed from the stimulus. Intense 

 stimulation of the tentacles of the medusa or of the margin of the bell 



induces, in Gonionemus, a direct contrac- 

 tion of the tentacles. 



When the margin or under surface of 

 the medusa bell is locally stimulated, the 

 manubrium behaves in a manner that is 

 of great interest. This has been described 

 by Romanes (1885) m tne medusa Tiar op- 

 sis indicans. If the margin or under sur- 

 face of the bell is sharply stimulated with 

 a needle, the manubrium at once bends 

 over and applies its tip to the point stimu- 

 Fig. 125.— The medusa Tiaropsis lated (Fig. 125). The reaction is thus 



indicans, applying its manubrium to a ■ i 1 t- i tt 1 



point on the margin which has been vel 7 precisely localized. How does it 



stimulated, x, y, z, cuts made for happen that the manubrium is able to 



experimental purposes. After Ro- 1 ^1^1 • 1 i 1 



manes (1885). locate exactly the point touched, and to 



bend at once in that direction ? 

 In answer to this question, Loeb presents a very simple explanation, 

 which deserves attention, as it is a type of many of the recent hypotheses 

 put forward to explain the behavior of organisms. According to Loeb, 

 this behavior is due simply to the spread- 

 ing out of the local contraction caused by 

 the stimulus. "Every localized stimulus 

 leads to an increase in the muscular tension 

 on all sides, which is most intense near the 

 stimulated spot. Now if we decompose 

 each of the lines of increase of tension 

 (aa' } ab', ac' ', ad', ae' Fig. 126) radiating „ „. .,, 



v ' .' . . . Fig. 126. — Diagram to illustrate 



from the Stimulated Spot, into a meridional Loeb's explanation of the localization 



component aa\ dd\ bb', etc., and an equa- aV^i^cToo) ^ manubrium - 

 torial component, it is evident that the 



latter can have no influence on the manubrium. Only the meridional 

 components can have an influence, and of these the one passing through 

 the stimulated spot is the largest. This fact must necessarily cause a 

 bending of the manubrium toward the stimulated spot" (Loeb, 1900, 



P- 32). _ 



This explanation represents the behavior as of the simplest character 

 — a mere spreading of a local contraction from the point stimulated. 

 But is this view adequate to explain the facts? In the protozoa we 



