Abstract
1. In calcium-free van't Hoff's solution and both Na-free and K-free mixtures having the other ions in the same proportion as in sea water at a pH of 7.1-8.0, the larvae of Bugula flabellata behaved exactly like those in sea water containing an excess of MgCl2. Phototropic reactions were lost, ciliated tissue was shed as material migrated basally from the pallial furrow and metamorphosis did not occur.2. In isotonic Mg-free solutions (pH = 8.0) metamorphosis was greatly accelerated, fixation occurring within 30 minutes to 3 hours in the majority of larvae; these organisms developed well-formed zooids in 10 hours. (Normally only about 77% of the larvae metamorphose by 12 hours.)3. Neutral red, methylene blue and, to a lesser extent, eosin accelerated metamorphosis. Neutral red, the most potent of the three, was effective in concentrations of 1:1,000,000 parts of sea water; methylene blue caused acceleration in concentrations of 1:500,000 parts. At a concentration of 1:100,000 parts of neutral red the average duration of the natatory period was about an hour.4. Metamorphosis failed to occur in Ca-free, Na-free and K-free media to which neutral red had been added in proportions of 1:100,000 parts. The same concentration of neutral red in isotonic Mg-free media (pH = 8.0) had a greater accelerating effect than when the dye was added to sea water in the same proportions. A reduction of temperature to 4° C. to 12° C. of sea water containing neutral red in parts of 1:100,000 antagonized the accelerating effects of neutral red. The staining reactions of neutral red and the problems involved in the study of metamorphosis are also discussed.
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