EXAGGERATED ELEVATION OF THE FERTILIZATION MEMBRANE OF CHAETOPTERUS EGGS, RESULTING FROM COLD-TREATMENT

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

1. Fertilized eggs of the polychaete annelid, Chaetopterus pergamentaceus, were cold-treated for various periods of time, ranging from 150 to 720 minutes, beginning immediately after insemination. Two general methods were employed; in one, the eggs were plunged into pre-chilled, filtered aerated sea water (2-3° C.); these experiments are referred to as involving temperature shock. In the other type, the eggs were gradually chilled to approximately the above temperature. At the end of the treatment period all eggs were allowed to return gradually to room temperature.

2. When eggs were cold-treated, with or without temperature shock, there was a pronounced asymmetrical exaggerated elevation of the vitelline membrane, which reached its greatest incidence about 40 minutes after the end of treatment, or shortly before the first cleavage. This exaggerated elevation continued in some cases after prolonged cold-treatment, so that the eggs were eventually denuded.

3. Most of the cold-treatments used were followed by delays in the first cleavage time for 50% of the experimental eggs as compared with 50% of the control population.

4. In all cases where cold-treatment was initiated with temperature shock, the effects on membrane elevation and cleavage time were much more pronounced than when the eggs were chilled gradually.

5. A number of characteristic morphological and cytological abnormalities were noted in embryos developing from the treated eggs; these included severe ciliary defects, fragmentation of the embryos, lagging or lost chromosomes or chromosome fragments, duplication of chromosome sets and/or individual chromosomes, suppression of polar bodies, and multipolar spindles.

6. It is suggested that the findings reported here afford evidence supporting Costello's (1958a) hypothesis that the rhythmic wrinkling and shape changes reported for the normal Chaetopterus egg by Pasteels may be due to the gradual release of some colloidal material from the surface of the egg. This release is considered to be blocked in some manner by the low temperature, and when the treatment is terminated, the release proceeds in a drastic, non-rhythmic manner; it then appears to be coupled with a change in the permeability of the vitelline membrane, so that the colloidal material is retained between the egg surface and the membrane. This brings about the exaggerated membrane elevation observed.