By this method fifty per cent. or more of the eggs of _purpuratus_ could be fertilized with the sperm of the starfish _Asterias ochracea, capitata_, Ophiurians, and Holothurians, while with the sperm of another starfish, _Pycnopodia spuria_, only five per cent., and with the sperm of _Asterina_ only one per cent. could be fertilized.[60] Godlewski succeeded by the same method in fertilizing the eggs of a Naples starfish with the sperm of a crinoid.[61] The writer did not succeed in bringing about the fertilization of the egg of another sea urchin in California, _Strongylocentrotus franciscanus_, with the sperm of a starfish. Although these eggs formed a membrane in contact with the sperm, the latter did not enter the egg; nor has the writer as yet succeeded in causing the sperm of _Asterias_ to enter the egg of _Arbacia_. [60] Loeb, J., _Arch. f. d. ges. Physiol._, 1903, xcix., 323; 1904, civ., 325; _Arch. f. Entwcklngsmech._, 1910, xxx., II., 44; 1914, xl., 310; _Science_, 1914, xl., 316. [61] Godlewski, E., _Arch. f. Entwcklngsmech._, 1906, xx., 579. Kupelwieser[62] observed that the spermatozoön of molluscs may occasionally enter into the egg of _S. purpuratus_ in normal sea water and later, at Naples, he observed the same for the sperm of annelids. In these cases no development took place. In teleost fishes the spermatozoön can enter the eggs of widely different species but with rare exceptions all the embryos will die in an early stage of development.[63] [62] Kupelwieser, H., _Arch. f. Entwcklngsmech._, 1909, xxvii., 434; _Arch. f. Zellforsch._, 1912, viii., 352. [63] See Chapter II. 2. The fact that an increase in the alkalinity or in the concentration of calcium allowed foreign sperm to enter the egg of the sea urchin, suggested the idea that a diminution of alkalinity or calcium in the sea water might block the entrance of the sperm of sea urchin into eggs of their own species. This was found to be correct; when we put eggs and sperm of the same species of sea urchin into solutions whose concentration of Ca or of OH is too small, the sperm, although it may be intensely active, cannot enter the egg.