CADET HAND 199 



they adhere to the shell. A few months ago, working at Banyuls 

 on the French Mediterranean Coast, D. Davenport, L. Sutton and 

 I looked at this phenomenon and satisfied ourselves that this initial 

 sticking of the tentacles was due to the discharge of nematocysts 

 (Davenport, D., D. M. Ross, and L. Sutton. 1961. Vie et Milieu, in 

 the press). I don't know what kind of nematocyst was involved so 

 I can't add anything about particular nematocyst types and their 

 functions, but certainly it was a nematocyst response to the shell. 

 Now that raises a puzzling point, because these tentacles of Calli- 

 actis stick very readily to shells when the anemone itself is not on a 

 shell; but if you pass a shell over the tentacles of a Calliactis that 

 is already on a shell, its tentacles do not stick. In other words, these 

 nematocysts seem, at any rate from this first observation, to be 

 affected b\' whether the anemone's foot is on the shell or not. 



We did some experiments to extend this observation. We had 

 20 Calliactis; 10 of them were settled on shells and 10 were lying 

 unattached on the floor of a tank. By taking a test shell and touch- 

 ing it to single tentacles around the disc, one can get a score of the 

 number of tentacles that stick. When the anemones are on the shell, 

 one gets a score of the order of 5 or less "tentacle-sticks" in 100 shell- 

 tentacle contacts. With the animals lying prone in the tank, one gets 

 a score of the order of 50 or more "tentacle-sticks" using the same 

 shell. In our experiments we transferred these same animals, al- 

 lowing those that had been unattached to settle on shells and strip- 

 ping off those that were attached so that the experiment could be 

 done in reverse. And then we got a good reversal of the scores; 

 the animals which were now on shells, which when unattached had 

 given scores of the order of 50, had now dropped to 5 or less, and 

 the other group, which when attached had given scores of 5 or less, 

 had now climbed up to about 50 "tentacle-sticks" per 100. To my 

 mind this phenomenon raises a crucial point as to whether nemato- 

 cysts are independent effectors or not. I say this because the only 

 change made in the experiment is that in one case the anemone has 

 its pedal disc attached to the shell, and in the other case the pedal 

 disc is free and unattached. So this observation forces one to con- 

 clude that the threshold for this kind of nematocyst discharge could 

 be affected by some form of remote control which in this case 

 seemed to originate in the pedal disc. 



