BEHAVIOR OF CCELENTERATA 201 



have found that such local action is as a rule not adequate; that the 

 organism tests the environment; and the behavior at a given moment 

 depends on the success or failure of a previous trial. Is there anything 

 of this kind in the medusa, or does Loeb's simple explanation exhaust 

 the matter? 



This question is clearly answered by the experiments of Romanes. 

 He found that if a cut is made parallel to the margin, as at x, Fig. 125, 

 and a point lying below this cut is stimulated, the manubrium is no 

 longer able to locate precisely the stimulated point. It bends, but no 

 longer directly to the point stimulated. This, according to Loeb, is 

 exactly what we should expect. The cut interrupts certain of the lines 

 of tension, so that they no longer pull the manubrium to the precise spot. 

 His explanation, he holds, " also shows why an incision parallel to the 

 margin of the umbrella makes an exact localization impossible and only 

 allows uncertain movements toward the stimulated quadrant" (1900, 

 p. 32). It is easy to see that the manubrium, on Loeb's theory of de- 

 composition of the lines of tension, would be pulled over in the general 

 direction of the stimulated spot, but might not strike it exactly. 



Is this what happens? Let us examine the facts as set forth in 

 Romanes' own words: "Although in the experiment just described 

 the manubrium is no longer able to localize the seat of stimulation in 

 the bell, it nevertheless continues able to perceive, so to speak, that 

 stimulation is being applied in the bell somewhere, for every time any 

 portion of tissue below the cut a is irritated, the manubrium actively 

 dodges about from one part of the bell to another, applying its extremity 

 now to this place and now to that one, as if seeking in vain for the of- 

 fending body. If the stimulation is persistent, the manubrium will 

 every now and then pause for a few seconds, as if trying to decide from 

 which direction the stimulus is proceeding, and will then suddenly 

 move over and apply its extremity, perhaps to the point that is opposite 

 the one which it is endeavoring to find. It will then suddenly leave 

 this point and try another, and so on, as long as the stimulation is con- 

 tinued" (Romanes, 1885, p. 112-113). 



From Romanes' description it is evident that the manubrium under 

 these circumstances may not even move in the general direction of the 

 point stimulated ; he says expressly that it may move toward the oppo- 

 site point, or toward any other point. At times, he says, a manubrium 

 moves from point to point, "without being able in the least degree to 

 localize the seat of irritation." The considerations adduced by Loeb 

 do not explain these facts; and his theory is quite inadequate to account 

 for the behavior. Contraction occurs, not merely as a direct spreading 

 from the point stimulated, but now in one place, now in another, 



