| Summary: | 1. Pieces of the mantle of Modiolus were sterilized by means of ultra-violet light, and cultivated, by the hanging drop method, in sea-water, and in sea-water plus tissue extract. 2. An outwandering of amoebocytes takes place shortly after the preparations are made; this is followed by an outgrowth from the epithelium which secretes the shell. Three types of epithelial cells are present in the outgrowths. 3. Undoubted stages of mitosis or of amitosis were not observed amongst the epithelial cells. 4. The shell epithelium often becomes folded so that hollows are present on the surface of the explant. The cells at the margin of the folds become elongate and tend to grow over the hollows. 5. The amoebocytes, by means of membranous expansions of the ectoplasm and fine pseudopodial-like processes, undergo movements and change of shape. Clumped and necrotic cells are rounded. 6. Hyaline and finely granular amoebocytes, due to their phagocytic action, become filled with granules, vacuoles, and large deeply stained bodies. 7. The amoebocytes often form a loose network in the medium. 8. Stages of mitosis or of amitosis were not observed, but amoebocytes with double nuclei were present in some of the preparations.
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