1. In corroboration of F. R. Lillie, it was found that the egg-secretions of Arbacia punclulata exert a chemotactic effect on sperm, and activate, agglutinate, and paralyze them. 2. The egg secretions of Asterias forbesii behave in a similar manner toward Asterias sperm. 3. Arbacia secretion activates, agglutinates, and paralyzes Asterias sperm, and Asterias secretion has the same effects on Arbacia sperm. 4. Paralyzed sperm may be reactivated but not reagglutinated. 5. The egg secretions test negatively for reducing substances and do not give the usual protein tests although they were found to be faintly positive to the acid tests and the xanthoproteic. This may be due to traces of the egg jelly. 6. Agglutination may be gotten with dry egg powder. 7. The agglutination reaction very possibly depends on a surface effect. 8. More soluble substances escape from the egg of Arbacia in hypertonic sea-water and in sea-water infected with sperm, than from unfertilized eggs in normal sterile sea-water in the same length of time. 9. The egg-secretion in certain concentrations retards development measurably. 10. 1.75 c.c. N/10 NaOH added to 100 c.c. of sea water does not accelerate the early cleavages. The retardation noted may well be within the limits of error. 11. NaOH in the same concentration does markedly accelerate the development of blastulæ into plutei. 12. Egg secretion in the concentrations employed+NaOH in the concentration given above, results in a more marked retardation of cleavage than the egg-secretion without the NaOH. 13. Egg-extract, as contrasted with egg-secretion, in addition to retarding development, in a similar manner when employed in a similar manner, results in cytolysis, arrests of development in the early cleavages, and a general failure of the eggs to get beyond the early non-motile blastula. 14. The heightened rate of oxidation in the fertilized egg; the increased rate of secretion in eggs undergoing fertilization; the decreased volume after fertilization all point toward the possibility that initiation of development depends upon the removal of substances, directly or indirectly antagonistic to oxidation. Proof that the egg-secretion in certain concentrations measurably retards development is however insufficient evidence either for the conclusion that it itself is the antagonist, or contains it. This would not follow even if it were shown that the retardation is the result of depressed oxidation. It is possible however that egg-secretion, at the moment of fertilization differs qualitatively from the earlier secretion, and contains the real antagonists whose inhibitory effect need not necessarily be thought of as having been direct. 15. These suggestions together with the facts upon which they are based, are not necessarily out of harmony with existing prominent theories of fertilization.