FACTORS INFLUENCING METAMORPHOSIS OF BUGULA LARVAE

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Abstract
Metamorphosis was inhibited by solns. containing 20 cc. sea water/80 cc. of iso-tonic KC1, MgCl2 and sucrose (pH=8.0) and in sea water below a pH of 6.0. Setting was greatly accelerated by the same proportions of sea water and isotonic CaCl2 at a pH of 8.0. In 20 cc. sea water/80 cc. isotonic NaCl the natatory period was abbreviated but only a small percentage of larvae metamorphosed. A 15 min. exposure of larvae to sea water diluted by 50% with . distilled water induced setting followed by normal development. In K-free, Ca-free and Na-free media, made by replacing the missing ion by isotonic sucrose (artificial sea water), the first stage of metamorphosis, eversion of the hold-fast, did not occur; the second stage, migration of tissue from the pallial furrow, was partially completed; the larvae behaved like those in sea water containing an excess of MgCl2- Setting was accelerated in Mg-free media. All solns. were at a pH of 8.0. Neutral red in concn. of 1:100,000-1:1,000,000 parts sea water (pH = 8.0) induced setting; methylene blue and eosin were less effective. Neutral red did not effect metamorphosis in Ca-free, K-free and Na-free solns., but is accelerated setting in Mg-free media. The potency of neutral red in sea water (1:100,000) was reduced by lowering the temp. to 4[degree]C. Two-ion combinations (without vital dye) indicated that Mg-ions are necessary for prolonged ciliary action and that these movements are favored by an absence of K ions. Similarities between factors causing acceleration and inhibition of metamorphosis and those producing stimulation and anaesthesia (theory of Ca release) are discussed. The staining reactions of the larvae are described.

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