ABSTRACT
One of the classic descriptions of the insemination process is that of F. R. Lillie (1911) in the egg of the annelid, Nereis. According to Lillie, there exists beneath the vitelline membrane of the unfertilized Nereis egg a wide cortical layer. He describes it as “a coarsely alveolar layer with homogeneous alveolar contents. The walls of the alveoli are continuous internally with the protoplasm of egg, and unite externally to form a protoplasmic layer applied to the vitelline membrane.” Within 2 or 3 min. after the attachment of the spermatozoon to the egg, an outpouring of jelly from the cortical alveoli occurs, so that in about 15 min. this layer is represented only by the perivitelline space and the delicate walls of the original alveoli crossing this space to the vitelline membrane. A fertilization cone rises from the egg surface, moves gradually across the perivitelline space, and comes in contact with the membrane beneath the sperm. After the retraction of the cone, the sperm head passes through the membrane into the egg. There is no discussion of the nature of the alveolar walls, nor is there any account of how these walls disappear even though they are not visible in many of the figures.
The writer wishes to express his gratitude to Profs. L. G. Barth and Robert Chambers for their generous help in the execution of the investigation and in the preparation of the manuscript.
