THE X-IRRADIATION OF MARINE GAMETES. A STUDY OF THE EFFECTS OF X-IRRADIATION AT DIFFERENT LEVELS ON THE GERM CELLS OF THE CLAM, SPISULA (FORMERLY MACTRA)

¹ Radiological Research Laboratory, Columbia University, New York N. Y., and Marine Biological Laboratory, Woods Hole, Mass.

1. The spermatozoa of the clam Spisula are more radioresistant than are its eggs.

2. The fertilizing power of Spisula sperm in the dry or concentrated state could not be affected by x-irradiation even to 264,000 r.

3. Increasing x-irradiation of Spisula spermatozoa caused increasing delay in cleavage time of normal eggs fertilized by such sperm, but the curve was not linear and did not exceed 15 minutes. This delay represents the time interval between the first and the second normal cleavages.

4. Trochophore production was at its lowest following 163,000 r x-irradiation of the spermatozoa, but with further x-irradiation trochophore production reached 95%. Such trochophores, while viable for a time, were not normal.

5. Dilution of Spisula spermatozoa increased their radiosensitivity as determined by the effect on subsequent embryonic development.

6. The demonstrated parthenogenetic stimulating ability of Spisula spermatozoa exposed to 189,000 r or more x-rays and used with Spisula eggs, could not be achieved when Spisula sperm were used with Arbacia eggs.

7. X-irradiated Spisula gametes exude a mucilaginous substance which causes them to aggregate (clump).

8. Very few Spisula eggs exposed to 189,000 r x-rays cleaved and none became trochophores. After 214,200 r there was evidence of cytoplasmic and membrane destruction.

9. Neither cysteine hydrochloride or B-mercaptoethylamine appeared to give any appreciable protection to Spisula gametes against x-irradiation as determined by the subsequent development of the embryo.