42 ORGANIZATION OF THE STARFISH EGG 



the spermatozoa quickly crowd about the egg as they are trapped in 

 the jelly surrounding the membrane. In a membraneless egg no 

 crowding of spermatozoa is noticeable and heavy insemination is 

 necessary to bring about fertilization. With such eggs, when a 

 cloud of sperm has been blown upon them, one may frequently observe 

 a spermatozoon swim toward an egg, wander over its surface and 

 then swim away. On the other hand the empty membrane with its 

 investing jelly immediately becomes covered with a halo of active 

 spermatozoa. 



The nucleus of the egg cell is a liquid drop surrounded by a mor- 

 phologically definite membrane. The nucleus may be moved about 

 within the egg with the needle, and can be considerably deformed by 

 pressure. On removal of the needle the nucleus quickly resumes its 

 spherical shape. Tearing the nucleus slightly causes the nucleus 

 to shrink and the nucleolus to disappear; this is followed by a remark- 

 able spread of a disintegrative process which involves the cytoplasm 

 surrounding the nuclear area. In the immature egg, where the nucleus 

 is large, the disintegrative process may extend throughout the entire 

 egg. In the mature egg with a relatively small nucleus the destruction 

 is restricted to a limited area. 



The disappearance of the nucleus or germinal vesicle during mat- 

 uration has been described by several investigators. The nuclear 

 membrane breaks down spontaneously and the nuclear sap spreads 

 slowly throughout the cytoplasm. So long as the nuclear area, 

 aside from the definitive egg nucleus, has not yet mixed with the 

 cytoplasm, I find that a puncture of the area starts up the disintegra- 

 tive process. When the nuclear sap has entirely mixed with the 

 cytoplasm, any part of the egg, with the exception of the minute egg 

 nucleus, may be torn with impunity. The mere presence of the glass 

 needle in the nuclear sap is not sufficient to start up the disintegrative 

 process. This process occurs only when the nuclear sap is agitated 

 by the needle while the sap is in direct contact with the cytoplasm. 



Wilson^ found in the Nemertine egg that any non-nucleated frag- 

 ment, prior to the dissolution of the germinal vesicle, is non-fertilizable 

 whereas, any fragment from a mature egg is capable of being fertilized 

 and undergoing cleavage. This I have found to be true also for the 



^ Wilson, E. B., Experiments on cleavage and localization in the Nemertine 

 egg. Arch. Entwcklingsmechn., 1903, xvi, 411. 



