STUDIES ON THE ORGANIZATION OF THE STARFISH 



EGG.* 



By ROBERT CHAMBERS. 



{From the Research Division of Eli Lilly and Company, Marine Biological Labora- 

 tory, Woods Hole.) 



(Received for publication, July 19, 1921.) 



The follovving is a preliminary record of operative work on the 

 starfish egg v/hich throws some light on the nature of the fertilization 

 membrane, the interaction between nucleus and cytoplasm, and the 

 relation of the cortex to the interior of the egg. 



By means of the microdissection needle it has been possible to 

 show that a morphologically definite membrane closely invests the 

 unfertilized egg, and that it is this membrane which lifts oft" upon 

 fertilization as the so called fertilization membrane. The description 

 of two methods will suffice to demonstrate this. By carefully pressing 

 an unfertilized mature egg between the surface of a cover-slip and the 

 side of a slender glass needle the egg may be cut in two without tearing 

 the investing membrane. This membrane now becomes apparent, 

 bridging the gap between the two egg fragments and holding them 

 together. Upon the addition of sperm this membrane lifts oft' as the 

 fertilization membrane, in such a way that the two egg fragments 

 come to lie within a single cavity. 



The unfertilized egg can also be slipped entirely out of its investing 

 membrane. Such an egg will undergo normal fertilization and cleave 

 into blastomeres having no investing membrane whatever. 



These two experiments definitely show that the normal unfertilized 

 starfish egg is already surrounded by a membrane which, upon fertili- 

 zation, becomes the fertilization membrane. 



The difference in behavior towards sperm of an egg, which has 

 been denuded not only of its jelly but also of its membrane, and one 

 which has not is very striking. In an egg enclosed in its membrane 



*Thc experiments reported in this paper constitute a part of the joint investi- 

 gation of the mechanism of fertilization in which Dr. G. H. .\. Clowes and the 

 writer are engaged. 



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