198 



THE BIOLOGY OF HYDRA : 1961 



ROSS:^ I would like to report some work which is partly on the 

 point of Dr. Hand's talk. 



By chance, a few months ago, I stumbled on a phenomenon 

 that I think has some bearing on the specialized function that certain 

 nematocysts can perform. The sea anemone, Calliocfis parasitica, 

 which I mentioned earlier today, lives on shells of hermit-crabs in 

 British and Mediterranean waters. About 2 years ago I found that 

 the anemone gets on the shell by a rather interesting behavior 

 pattern ( Fig. 1 ) . It will transfer from another surface to the shell by 

 a maneuver which begins with the adhesion of the tentacles to the 

 shell; subsequently the animal detaches the pedal disc which then 



Fig. 1. Calliactis parasitica adhering to shell by tentacles and (a) detach- 

 ing pedal disc from plastic plate and (b) swinging detached pedal disc over 

 towards shell for eventual settling. 4 min. between (a) and (b). 



(From Ross, D.M. 1960. Proc. Zoo/. Soc. London, 134: 43-57. Reprinted 

 by the courtesy of the Society) 



swings over and settles on the shell (Ross, D.M. (1960). Pwc. 

 zool. Soc. Lond. 134: 43-57). But the important point to which I 

 wish to draw attention is this initial response of the tentacles when 



iDr. Donald Ross, Department of Zoology, University of Alberta, Edmonton, Alberta, 

 Canada. 



