116 



G. H, PARKER 



see in the region of activity that each part of the disc was suc- 

 cessively hfted off the glass, advanced, and put down again. 

 This was suspected to be the case in Sagartia and has been inti- 

 mated for Metridium by McClendon ('06). 



The accompanying diagram (fig. 1) illustrates the steps by 

 which these waves may give rise to actual locomotion. At stage 



B 



C 



D 



E 



Fig. 1 Diagrammatic side-view of the foot of a creeping actinian illus- 

 trating the passage of a locomotor wave from one period of rest {A), through a 

 period of activity {B, C, D) to a second period of rest (E). Fixed points on 

 the substratum are numbered 0, 5, 10, 15, and 20. Points in the actinian that 

 at the beginning were opposite the fixed points 5 and 10 in the substratum are 

 numbered also 5 and 10. 



A a pedal disc is supposed to be at rest on the substratum, and 

 corresponding points in the disc and on the substratum are simi- 

 larily numbered. At B the locomotor wave has made its ap- 

 pearance at the posterior edge which has been lifted off the sub- 

 stratum and moved forward. At C the wave has reached the 

 middle of the disc and the posterior part has reattached itself in 



