FACTORS INFLUENCING METAMORPHOSIS OF BUGULA LARVAE

¹ St. Ambrose College, Davenport, Iowa, and the Marine Biological Laboratory, Woods Hole, Mass.

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.