Regeneration in youngBunodactis verrucosa Pennant (actinaria, anthozoa)

YoungBunodactis verrucosa Pennant at the 12 tentacle stage are employed to test the applicability of the polar coordinate model to coelenterate regeneration. The animals are cut along every radius into fragments of 3 to 9 segments. Most fragments are patent 3-4 weeks later, but small fragments have a higher mortality rate than large fragments. Some fragments do not regenerate and occasionally tentacles fuse, thereby reducing the number of segments. Small fragments tend to regenerate more tentacies than large fragments, but large fragments may regenerate great numbers of supernumerary tentacles. Twenty-two percent of the fragments restore the missing number of tentacles, while 76% of all fragments produce an even number of tentacles.Fragments restoring the correct numbers of tentacles show a marked tendency to form the correct tentacles (regulative regeneration). Fragments regenerating two less than the number of tentacles already present show a marked tendency to reproduce tentacles of the types already present (miror image formation). Other fragments produce missing segments (forward regeneration), or those already present (reverse regeneration) at lower frequencies.No fragments beginning or ending with the number 1 directive tentacle fail to regenerate entirely, while first cycle segments maximally remote from segment 1 are associated with the absence of regeneration. No fragments beginning or ending with the number 4 directive tentacle fail to undergo forward regeneration, regulate or produce a mirror image when the appropriate number of segments are regenerated. In contrast, segment 4 is associated with a low frequency of reverse regeneration, and second cycle segments cut away from immediate contact with segment 4 show an increase in the frequency of reverse regeneration. Controls through morphogenic substances rather than polar coordinates seem to explain these results. Such substances would control the number and direction of tentacle regeneration.