I n a paper entitled " T h e Influence of Light on the Development of Organs in Animals," '95, Loeb states "that light favors the development of polyps in Eudendrium (ramosum); that no polyps, or only very few, are developed in the dark." At the suggestion of Prof. Morgan, I undertook to determine the minimum amount of light required by this hydroid to regenerate its polyps. T h e experiments were conducted during the summer of 1905 at the Marine Biological Laboratory, a t Wood's Hole, Mass., while occupying a room of the Carnegie Institution.
EXPERIMENTS ON EUDENDRIUM RAMOSUM
Preliminary Experiments
Vigorous colonies of Eudendrium ramosum were selected. These consist of a main stem or stock and its branches. These primary branches in turn give rise to secondary and tertiary branches bearing polyps at their distal ends. These polypsand gonads when present-were separately cut off. T h e decapitated colony was placed in a glass bowl containing about 200 cc. of normal sea water. These bowls were allowed to remain in the light for fifteen, thirty, sixty minutes, respectively. At the expiration of each of these periods the bowls were placed in a dark chamber, from which all light was carefully excluded. Other series, of six bowls each, prepared in the same way were placed in the dark immediately after the removal of the polyps. After forty-eight and seventy-two hours, respectively, each series was exposed to the light as above mentioned.
I n the following tables, the numbers indicate the regenerated hydranths which have free and distinct tentacles.
Tables A, B and C indicate results of these experiments.