Entrance of Spermatozoon into Starfish Egg 137 

 67 (2027) 



A note on the entrance of the spermatozoon into the starfish egg. 

 By ROBERT CHAMBERS. 



[From the Department of Anatomy, Cornell University Medical 

 College, New York City.] 



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 de- 

 tails 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 sur- 

 face of the jelly stick and are unable to penetrate it to any ex- 

 tent. 



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 sus- 

 pension 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 fila- 



