COMPLEX RESPONSES 167 



With the exhaustion of the given marginal body, the con- 

 trol naturally passes to the most active of the remaining 

 bodies. Thus the rate of pulsing would be determined 

 first by one, then by another marginal body, depending 

 upon the temporary physiological state of these parts. 

 Hence this type of rhythmic activity presents no element 

 that calls for centralized control, a condition that would 

 be difficult to harmonize with what is known of the nerve- 

 net. It is the result rather of the state of the marginal 

 bodies which, as von Uexkiill (1901) has shown, can be 

 thrown into action by so slight a movement as that pro- 

 duced by the elastic recovery of the bell after its pulse. 



Another form of response that may be taken as indic- 

 ative of the nature of the nerve-net in actinians is loco- 

 motion. Gosse (1860), a most enthusiastic and industri- 

 ous student of these animals, after watching the creeping 

 of Sagartia pallida, wrote that "it was impossible to wit- 

 ness the methodical regularity of the process, and the 

 fitness of the mode for attaining the end, without being 

 assured of the existence of both consciousness and will 

 in this low animal form." Such an opinion, however, 

 was rather the result of an admiring devotion to an in- 

 teresting group of animals than to a close scrutiny of 

 their real performances, especially under experimental 

 conditions. Pedal locomotion has already been discussed 

 in an earlier chapter of this book where it was pointed 

 out that this operation could be successfully performed 

 by specimens of Sagartia from which the oral half had 

 been cut away. Such fragments not only creep but creep 

 away from the light as normal individuals do. In fact, 

 their activities are not essentially different from those 

 of whole animals. Creeping, then, is in no sense depen- 

 dent upon the animal as a unit, but is an activity of the 



