FURTHER EXPERIMENTS ON THE EFFECT OF HEAT ON THE EGGS OF CUMINGIA

Abstract

1. If the eggs of Cumingia are subjected to heat immediately after fertilization, they do not form polar bodies. The chromosomes of the first polar spindle divide and two resting nuclei are formed. These nuclei fuse with each other and with the male pronucleus, giving rise to a cleavage nucleus which contains a triploid amount of chromatin.2. The equatorial plates of these eggs show forty-five to sixty chromosomes. About the same number has been found in the cleavage of parthenogenetic (diploid) eggs; but there the individual bodies are smaller than they are in the triploid eggs.3. If fertilized eggs are heated after they have formed polar bodies, the equatorial plates of their first cleavage contain fifty-five to sixty-five chromosomes. These are equal in size to those of a triploid egg.4. Study of later stages (resting nuclei and equatorial plates) shows that the chromatin of the polar nucleus is active, and approximately equivalent to that of a male pronucleus.5. The size and number of the chromosomes in heated eggs is not dependent on the amount of chromatin that is present. They vary with the susceptibility of the egg to heat.6. The conditions described are not in opposition to the theory of the individuality of the chromosomes, if that theory is given a broad interpretation.