FORM-REGULATION IN CERIANTHUS, VIII

Abstract

1. Supplementary partial discs with a number of tentacles corresponding to that portion of the whole circumference which they represent can be produced from lateral transverse cuts in the body-wall of Cerianthus.2. If the lateral cut is in the œsophageal region and is deep enough to involve the œsophagus the supplementary disc possesses a mouth because the cut surfaces of the body-wall unite with the cut surfaces of the œsophagus, thus forming a second opening into the œsophagus. If the cut is below the œsophageal region the supplementary disc possesses no mouth. In the extreme aboral region of the body the formation of supplementary discs does not occur.3. When the lateral cut is made in the œsophageal region the permanent collapse and atrophy of the tentacles and region directly above the cut occurs, or if these have been removed their regeneration is retarded and atrophy occurs after a time. This collapse and atrophy is due, not to loss of intracellular turgor but to decrease in the internal water-pressure since the enteric cavity of the region above the cut is completely shut off from the general enteric cavity and from the exterior.4. In two cases the formation of tentacles on the aboral end of a piece of certain form was observed. In both of these cases the conditions of internal pressure were apparently similar to those which exist at the oral end, but the less rapid regeneration of the aboral tentacles indicates either a difference in structural relations at the two ends or a difference in "polarity."