POLAR BODY EXTRUSION AND CLEAVAGE IN ARTIFICIALLY ACTIVATED EGGS OF URECHIS CAUPO

¹ From the William, G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California

1. Urechis eggs activated by prolonged exposure to ammoniacal sea water give a high percentage of cleavage as Hiraiwa and Kawamura showed, but such exposures also give a high percentage of polar body suppression.

2. Isolation of eggs of known polar body history shows that practically all those eggs divide that fail to extrude the first or the first and second polar bodies, but only a small percentage of those eggs that extrude the first and second polar body.

3. Eggs that fail to extrude the first polar body may produce two, one or no polar bodies at the time when the second polar body should appear. Later, two, three or four nuclei are visible in the egg corresponding to whether two, one or no polar bodies are present. The first cleavage of these three types gives two, three or four cells respectively.

4. Eggs that extrude the first polar body almost invariably produce the second.

5. Determinations of the time of polar body appearance after various lengths of exposure indicate that not more than four or five minutes progress toward polar body extrusion is made during sojourn in the solution, whereas other developmental changes progress further.

6. Eggs that had been given the kind of first treatment that results in 100 per cent normal polar body formation but no cleavage could not be induced to divide by a second treatment applied at various times after the extrusion of the second polar body. Cleavage was, however, obtained when the second treatment was started before the time of extrusion of the second polar body.

7. The "poorly activated" type of egg that divides without polar body formation or evidence of submerged maturation division is obtained by short exposures to ammoniacal sea water, to ammoniacaldilute sea water, or to acid sea water, the second agent giving the highest percentages. The first cleavage is into two cells.

8. Normal development is obtained when "blocked" fertilized eggs are activated with the treatment that ordinarily results in 100 per cent polar body formation but no cleavage. Also superposition of fertilization after such treatment results in normal development.