1. The view is confirmed that the zona pellucida is not an essential factor in the formation of the fertilisation membrane (pp. 96–100).
2. Partial activation of the eggs of Asterias rubens is described with the formation of Seifriz's “protoplasmic papillæ” (pp. 100, 101).
3. Artificial activation of the eggs of Asterias rubens by isotonic solutions of NaCl, KCl, CaCl2, and MgCl2 is described. It was found that decrease in surface tension is not a necessary factor in causing artificial membrane formation (pp. 102–104).
4. The influence of the hydrogen ion concentration of the medium on the degree of extrusion of the fertilisation membrane of Echinus miliaris has been examined, and indicates that osmotic pressure due to the presence of a protein within the membrane is responsible for the extrusion (pp. 105–109).
5. From a study of the influence of salt concentration on the extrusion of the fertilisation membrane of Echinus miliaris, it is concluded that the fertilisation membrane is, from the moment of its formation, completely permeable to salts (pp. 109–112).
6. The origin of the fertilisation membrane has been examined, but in the absence of critical evidence it is concluded that the question cannot be regarded as settled (pp. 112–114).