1. The swimming behaviour of the anemone Stomphia coccinea, previously known to be a specific response to contact with two species of starfish, is briefly described.
2. The sphincter, isolated or intact, gives a reflex quick contraction when the tentacles are stimulated with whole Dermasterias imbricata or with extract, but not when other starfish are used. Sphincter preparations stimulated electrically give a quick facilitated contraction at frequencies above 1 in 3 sec., and slow contractions at fre quencies below 1 in 2 sec. Quick and slow contractions appear to have the same threshold, which is unaffected by the presence of starfish extract. Possible attributes of the chemosensory system are discussed.
3. Elongation of the column is an essential preliminary to swimming, whereas detachment from the substratum, due mainly to contraction of the parieto-basilar muscles, does not always occur. Cutting experiments, and orientated recording of the swimming movements which ensue, suggest that excitation is maintained locally in the column, and that the parieto-basilar and circular muscles function synergically. Multipolar nerve cells in the column may be concerned with this activity.
4. Various special features of the anatomy of Stomphia may be correlated with its ability to swim.
5. Although the origin and adaptive value of the swimming response are still scure, it is clear that it must be of distinct biological advantage to the species.
It is a pleasure to thank the U.S. Office of Naval Research (Biology Branch) for financial support which enabled this work to be carried out; Dr D. L. Ray for the privilege of being much indebted to her; the Director of the University of Washington Marine Laboratories at Friday Harbor and his staff and colleagues for their assistance; Dr H. Fraser-Rowell for taking photographs for P1. I A and B; and Prof. C. F. A. Pantin, F.R.S., and Dr E. W. McConnachie for helpful criticism of the manuscript.
A tribute to William N. “MAC” McFarland
(1926–2004)