THE EFFECT OF LOW TEMPERATURE AND OF HYPOTONICITY ON THE MORPHOLOGY OF THE CLEAVAGE FURROW IN ARBACIA EGGS

¹ Department of Biology, Union College, Schenectady, N. Y. and The Marine Biological Laboratory, Woods Hole, Massachusetts

1. Under certain conditions the eggs of Arbacia punctulata develop a cleavage stalk between the first two blastomeres. No stalk forms in sea water if the temperature is in the 20° C. to 30° C. range; low temperature (10° C.) causes the development of a stalk in sea water; a short stalk develops in isotonic calcium-free sea water at 20° C.; a very long stalk develops if eggs are cleaving in hypotonic sea water (65 per cent).

2. The effect of the above treatments on the appearance of cleaving dispermic eggs is described.

3. Evidence indicates that stalks of 8 micra diameter are all gel, yet in hypotonic sea water they continue to constrict and elongate. This is good evidence that the cortical gel has inherent contractile properties.

4. It is hypothesized that any event which deforms the Arbacia egg (if it is in the "cleavage phase") leads in some way to an orientation of contraction around the isthmus. The deforming force may be an enlarging aster, an elongating spindle, or an endoplasmic flow.