If several spermatozoa become attached to the vitellus at the same instant membrane elevation starts at each point of attachment no matter what the distance separating them. The observer is indeed struck with the rare occurrence of polyspermy even with heavy insemination. Two minutes after insemination. Membrane is fully rounded, equidistant from all points from the now spherical egg. About the same time as in Fig.
Cone is clearly visible.
Ten minutes after fertilization. The heads of those still farther away but not far enough beyond the area of decrement actually to be engulfed are likewise afffixed and present a swollen appearance. When the membrane lifts off these afffixed sperm are carried with it. The Echinarachnius egg, then, would seem to be unusual, since a gradient of susceptibility to the sperm may actually be demonstrated in the cortical changes following sperm entry. Experiments are being made at present with the hope of analyzing farther these cortical responses of the Echinarachnius egg to the sperm.