THE EFFECTS OF X-IRRADIATION ON THE FERTILIZED EGGS OF THE ANNELID, CHAETOPTERUS

¹ Marine Biological Laboratory, Woods Hole, Mass., and Department of Zoology, University of North Carolina, Chapel Hill, N. C.

1. Fertilized eggs of Chaetopterus were x-irradiated, beginning 30 minutes after insemination; doses from 255 r to 17,280 r were used, and the duration of treatment was one-half minute to eight minutes. Observations were made of both living and fixed eggs, at various intervals after irradiation, and of living trochophore larvae 19-22 hours after irradiation.

2. The principal effects of relatively low doses (255-1020 r) were found to be a slight retardation of cleavage (3-5 minutes), and the production of abnormal trochophore larvae which were characterized by severe ciliary defects, cytoplasmic blebs, and very feeble movements (following doses of 255 to 765 r). Doses of 1020 r and above resulted in death of most of the larvae by the trochophore stage. The majority of the eggs irradiated with 1275 r and above showed at least a slight retardation of the first three cleavages.

3. Among the cytological abnormalities observed (especially after the higher doses) were multipolar spindles, chromosome fragmentation, and karyokinesis without cytokinesis.