Studies of the obelia medusa with special reference to its reactions to light

Abstract

The thesis gives a brief review of the literature dealing with the reactions to light of various Hyrdo-medusae and proceeds to a study of the controversy surrounding the subject of the "ocelli" of the Lepto-medusan Obelia and to a statement of the results of an investigation into the cytology of the basal bulbs of the tentacles of this medusa. The main body of the thesis is devoted to the experiments which were carried out in order to determine the reactions of the Obelia medusa to light under varying conditions in the laboratory, with the results of the experiments, and with their interpretation leading to the conclusion that light acts as a constant stimulus to Obelia which exhibits negative phototaxis. The reactions of Obalia have been compared with those of the anthomedusan leuckartiara throughout. A discussion of the rudimentary condition of the velum in Obelia precedes the summary which concludes the paper.