It is probable that in this case the mechanism of fertilisation is essentially the same as in the case where the membrane-formation is brought about, with this difference only, that the cytolytic effect is less when no fertilisation-membrane is formed.
"Darwin and Modern Science"
A.C. Seward and Others
Presumably some blood enters the eggs and causes the cytolytic effects in a less degree than is necessary for membrane-formation, but in a sufficient degree to cause their development.
"Darwin and Modern Science"
A.C. Seward and Others