A NEW METHOD OF PRODUCING TWINS, TRIPLETS AND QUADRUPLETS IN ARBACIA PUNCTULATA, AND THEIR DEVELOPMENT

¹ From the Marine Biological Laboratory, Woods Hole, and the Biological Laboratory, Princeton University

1. Twins, triplets, and quadruplets of Arbacia punctulata are obtained by treating the eggs just after first and second cleavage with a hypertonic salt solution, which thickens the ectoplasmic layer; the blastomeres separate when returned to sea water. The blastomeres develop independently but attached to each other until they become free-swimming blastulae, when they can be isolated in pairs or quartets.

2. Twins, triplets and quadruplets from a single egg may all develop into perfect dwarf plutei.

3. There is no indication of any differences among the twins, triplets, and quadruplets of a set (i.e. from one egg) caused by the segregation of any special organ-forming materials by the first two cleavage planes, nor by a separation into a right and left half, or into an anterior and posterior part.

4. Differences and abnormalities in the development of twins, triplets, and quadruplets are probably caused by experimental conditions or by differences in vitality of the original egg, since abnormalities of the same sort occur among the controls, and since some lots develop much better than others.

5. Twins may also be obtained by centrifuging the eggs just after first cleavage. The ectoplasmic layer is centrifuged off, and the two blastomeres develop independently but attached to each other until they become free-swimming blastulae. Both twins may form perfect dwarf plutei.

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