THE METAMORPHOSIS OF PARTIAL LARVAE OF PERONELLA JAPONICA MORTENSEN, A SAND DOLLAR

¹ Department of Biology, Tokyo Metropolitan University, Meguro-ku, Tokyo and Misaki Marine Biological Station, Misaki, Kanagawa-ken, Japan

1. In the larva of the sand dollar Peronella, the mouth does not open, and no functional digestive tract is formed so that no feeding is necessary before metamorphosis.

2. Both the amniotic cavity and the hydrocoel take a median position in the larval body.

3. Cutting experiments show that single blastomeres of the two- or four-cell stage are totipotent regarding metamorphosing capacity.

4. Any meridional half of the larval stages has the capacity for metamorphosis.

5. The vegetal half of the sixteen-cell stage metamorphoses, but the animal half develops only to the blastula stage.

6. The vegetal halves, but not the animal halves, of the blastula and gastrula stages are able to metamorphose.

7. Both anterior and posterior halves of the pluteus stage are able to metamorphose.

8. The percentages of metamorphosis of partial larvae fall to a minimum at the gastrula-stages after which they rise while the regulative capacity falls as a course of a steady decrease.

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