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An egg-membrane lysin was partially purified from the sperm extract of Tegula pjeifjeri. A turbidimetric and a chemical method with the use of isolated egg membrane as the substrate have been proposed for the quantitative assay of the lysin. The methods are shown to be valid over a limited range of lysin concentration.The pH optimum for the lytic activity is at about 8.3. The lysin shows considerable thermo-instability and is highly sensitive to PCMB and heavy metals. The reduction in turbidity of egg-membrane suspensions during lysis is accompanied by the release of a substance(s) containing neutral sugar.The possibility that the lytic process is composed of two steps is discussed.Two methods are routinely used t o evaluate the lytic activity of a sperm extract: one method is based on the calibration of the time required for complete disappearance of the egg membrane of the whole egg (TYLER, 1939) or of isolated egg membrane (BERG, 1950) and the other, more complicated but more sensitive, is the "indentation method", in which the number of indentations appearing on an egg membrane during lysis is counted at fixed intervals (KRAUSS, 1950). Although some properties of the lysin obtained from Mytilus o r Megathum sperm have been clarified by these methods, they are too qualitative t o serve as a tool for the quantitative characterization of a lysin or its mode of action.In a previous paper (HAINO and KIGAWA, 1966), we have reported a method for isolating the egg membrane from ovaries of Teguia pjeijyeri, and have also reported on chemical analyses which revealed that the egg membrane is composed of protein and sulfated mucopolysaccharide. During the course of these studies, two reaction processes were found t o provide methods for the quantitative assay of the lytic activity: (1) reduction of turbidity during lysis of a suspension of finely fragmented egg membranes; (2) liberation of some pro-203

Although it has been known for some time from morphological evidence (DAN, 1952; AFZELIUS and MURRAY, 1957) that the acrosome of the sea urchin spermatozoon reacts to the presence of the jelly substance of its own species by forming a delicate process'], the only quantitative evidence bearing on this subject to be presented so far is that of COLLIER (1959). Working with Strongylocentrotus purpuratus, he found that about 60% of the spermatozoa suspended in a solution of jelly substance ("homologous fertilizin") underwent such a reaction, in contrast to about 10% of those suspended in sea water. His results also show that the percentages of reacting spermatozoa tend to increase as the concentration of fertilizin rises.Preliminary experiments performed on Hemicentrotus gametes in collaboration with E. NAXANO, and on gametes of Lytechinus variegatus, with C. B. METZ a t the Alligator Harbor Laboratory of Florida State University, indicate similar trends in these species. The experiments to be reported here are a continuation of that work; while they more or less repeat those of COLLIER, t h e authors feel that the confirmation of his results with different material sufficiently justifies their publication. MATERIAL AND METHODSThe sea urchins used were the regular urchins Pseudocentrotus