THE EFFECTS OF ULTRA-VIOLET RADIATION OF 2537A UPON CLEAVAGE OF SEA URCHIN EGGS

¹ From the School of Biological Sciences, Stanford University

1. There is a threshold dosage between 10¹⁰and 10¹¹ quanta below which radiation of 2537A produces no observable change in the rate of cleavage. Beyond this threshold the degree of retardation increases with the dose.

2. Many of the retarded eggs develop normally, but are slower in reaching a given stage; others continue developing for only a short time, the degree of differentiation reached being inversely proportional to the dosage.

3. Unfertilized eggs, eggs 15 and 90 minutes after insemination, and eggs in the first cleavage do not exhibit strikingly different susceptibilities to the rays, although the later stages appear to be some what more susceptible.

4. The quantity of radiant energy which the eggs can absorb before being affected is quite large, as indicated by the extinction measurements reported, and serves as a rough measure of the power of repair of the egg protoplasm.

5. A series of dosages from a dose which cytolyzes to one which has no retarding effect upon cleavage with light of 2537A failed to induce artificial parthenogenesis.

6. No evidences were obtained over the dosage series investigated for acceleration of the rate of cleavage.