46 INVERTEBRATE PHYSIOLOGY 



done in the 1955 invertebrate course at Wood's Hole failed to show any 

 obvious specificity in anthozoans. This difl^erence might possibly be linked 

 to the apparent differences in the nerve-net properties of Hydra and those 

 other members of the phylum that have been investigated (see Pantin, 

 1950) ; on the other hand, it may be that other fresh- water hydrozoans 

 are also glutathione sensitive. 



A number of different coelenterates have "phases" of rhythmic feeding 

 activities. According to Jennings (1906) : 



. . . green Hydra, undisturbed, show rhythmic activity. Every minute or two it con- 

 tracts and then extends in a new direction. In this way the animal explores the region 

 about its place of attachment and largely increases its chances of obtaining food. This 

 motion seems to take place more frequently in hungry individuals, while in well fed 

 specimens it may not occur. 



Also Torrey (1905) and later Parker (1917b) showed that the solitary 

 hydroid Corymorpha shows a "nodding" behavior every 2^/^ to 3 minutes, 

 moving the hydranth down to the substrate by bending the stalk and then 

 puUing the tentacles along the bottom. This activity is suppressed by caus- 

 ing water to flow over the tentacles, but is continued by both decapitate 

 stalk and isolated hydranth, although at a shiver rate, when these parts 

 are isolated. Here it would look as though inherent rhythms of nervous 

 activity, in each part, reinforce each other in the intact animal, while higher 

 levels of activity, such as that caused by continual tentacular stimulation, 

 inhibit the rhythmic pattern. One would expect that it would be valuable 

 to analyze these cases more closely in the way Batham and Pantin have 

 investigated M etridimn. 



The most pressing general problem that needs to be attacked experi- 

 mentally and analytically is : How are these "inherent activity" phases 

 initiated and modified by changes in the environment, both external and 

 internal? The truth would seem to include both Parker's (1917b) "... 

 behavior is chiefly determined by their immediate environment," and 

 Jenning's (1906) "...complex movements and changes in movement 

 may occur from internal causes, zvithout any change in the environment" 

 (my italics). Immediate environmental stimuli not only have a direct 

 effect on actinian behavior but also lead to slow long-lasting changes in 

 "inherent activity" and in the "phase" of activity. We must find out how 

 these environmental changes are detected by the organism and what are 

 the corresponding changes in the level of nervous activity. To put it an- 

 other way, what slow changes in the "background level" of nerve-net- 

 activity occur? Some coelenterates may have inherent "built in" back- 

 ground level maintainers, such as Corymorpha, the green hydra, and 

 possibly scyphozoans with tentaculocysts ; and other forms may depend on 

 external stimuli, such as tide-pool currents (Parker, 1917a) for Metridium 



