Abstract
In 1876 Fol made the classic discovery that the spermatozoon actually enters the egg in fertilization. This fact he observed in the starfish egg. Fol's treatise was apparently so exhaustive and so carefully worked out that no one has questioned the details of his observations and his interpretation of the process is generally accepted to this day. Conical elevations were seen to form on the surface of the egg and the spermatozoa travelled in a straight line toward them. When a spermatozoon reached a cone its head penetrated it. Fol called the conical elevation the “attraction cone” and believed that it attracted the spermatozoon from a distance.
The starfish egg is surrounded by a zone of glutinous jelly the thickness of which is about one fifth the diameter of the egg. When the eggs are placed in a sperm suspension all the spermatozoa that accidentally come into contact with the surface of the jelly stick and are unable to penetrate it to any extent.
My observations confirm those of Fol regarding the formation of the cones on the egg's surface. The number of cones depends upon the age of the egg and upon the density of the sperm suspension surrounding it. An overripe egg forms these cones quickly and in considerable numbers. A fresh mature egg forms only a few cones unless the sperm suspension is very dense.
Fol, however, failed to observe the following: From the tip of each cone a slender filament grows outward piercing the jelly until it reaches the periphery where the trapped spermatozoa are lying. If there be no spermatozoa in the immediate vicinity nothing more happens. If, however, the tip of the filament comes into contact with a spermatozoon the cytoplasm of the tip and that of the sperm head immediately flow together so that the sperm nucleus now lies within the cytoplasm of the egg filament.
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