PREY-PREDATOR RECOGNITION 



43 



manes, Loeb, Parker, and Pantin. Finally, these generally carnivorous 

 animals are either, for our purposes of the moment, sessile forms, or 

 passively floating or swimming organisms ; in other words, they do not 

 "hunt down" their prey. The well-known "fishing" behavior shown by 

 certain medusae, the trachyline medusa Gonionemus (Yerkes, 1902) for 

 example, seems more nearly related to the "slowly" waving tentacles of 

 sea anemone or hydra than to any example of directed hunting. 



Pollock (1883), a colleague of Romanes, appears to have been the first 

 to recognize that anemones respond to weak chemical stimulation. His 

 observations were confirmed and extended by Nagel (1892), Loeb (1918, 

 for resume), Jennings (1906), and Batham and Pantin (1950a,b). The 



•Q^ 



f 



Fig. 1. Appearance of Mctridium during various phases: a, specimen ingesting 

 food; b, typical appearance J4-J^ hour after food ingestion; c, d, swaying movements 

 6 hours after food-extract stimulus ; e, f, g, successive stages in antiperistaltic con- 

 striction, leading to defecation; and h, "shrivelling." From Batham and Pantin, 

 1950b. 



latter authors, in giving us the most complete available analysis of the 

 various activities of sea anemones we have, in Metridium, differentiated 

 different "phases" of "inherent activity"^ that may follow feeding or 

 stimulation by food extracts without subsequent reward. As a result of 



2 By "inherent activity" these authors mean that ". . . the activity is an observed 

 property of the animals which does not arise directly from external stimuli" (1950a, 

 p. 299) . It is clearly not a simple chain reflex. 



