THE ORIGIN AND NATURE OF THE FERTILIZATION MEMBRANE IN VARIOUS MARINE OVA

Abstract

The morphological changes in the development of the fertilization membrane have been described and figured in the text. 1. Examination of the vitellus of the unfertilized egg by means of the micropipette and by the microdissection method indicate that a surface layer (the vitelline membrane) is demonstrable on eggs of the forms studied. For Dendraster and Strongylocentrotus the superficial layer is a soft, flexible, gelatinous substance. In contrast to this, eggs of Patiria and Urechis are enclosed by a definite tough membrane. 2. In every case the fertilization membrane is developed from the superficial layer of the unfertilized egg. In the sand dollar and sea urchin this takes place by a radical transformation and alteration of the surface layer. For the starfish and Urechis the process is essentially a separation of the tough outer layer (the egg membrane) and its transformation into the fertilization membrane. 3. The superficial layer of the unfertilized egg properly may be considered a precursor to the fertilization membrane. This is splendidly shown in the microdissection and centrifuge studies on eggs of the sand dollar where the development of the fertilization membrane is greatly modified. 4. Changes in the consistency and properties of the fertilization membrane occur. These changes may be correlated with stages in the development of the membrane. They offer further substantial proof that the vitelline membrane and the fertilization membrane are not identical. 5. That the fertilization membrane is actually a structure which is developed as a consequence to the activation of the egg is shown by its difference from any pre-existing structure on the unfertilized egg. 6. From the evidence presented it is concluded that eggs fall into two general categories, namely, a group in which the fertilization membrane is developed in large part from a pliable superficial layer of substance; and a group in which the fertilization membrane is developed by the separation from the egg of a tough pre-existing membrane.