44 ORGANIZATION OF THE STARFISH EGG 



described by the writer.^ If the surface of the mature starfish egg 

 be torn with a needle, and the egg then caught at the opposite side 

 and pulled to the edge of the hanging drop, the compression on the 

 egg produced by the shallow water at the edge of the drop will 

 cause the fluid interior to ooze out through the tear, forming a perfect 

 sphere. One may so manipulate the process as to cause the egg 

 nucleus either to remain behind in the cortex (the cortical remnant) 

 or to pass into the extruded sphere. 



The cortical remnant is relatively solid and remains more or less 

 enclosed within the egg membrane and its jelly. If left long enough 

 it will eventually round up so as to present the appearance of a dimin- 

 utive egg surrounded by a collapsed and wrinkled egg membrane. 



The material which has escaped from the egg into the sea water 

 is fluid and tends immediately to round up. On tearing with a needle 

 its surface behaves like that of a highly viscous oil drop. These spheres 

 adhere tenaciously to glass and, in the effort to remove them by 

 blowing a current of water against them, they sometimes leave a torn 

 off piece behind. The cortical remnant is readily fertilizable and 

 undergoes normal segmentation. On the other hand, the material 

 which has escaped from the interior of the egg whether nucleated or 

 not, i? non-fertilizable. It remains inert until it finally undergoes 

 disintegration. As long as it possesses an intact surface it appears 

 exactly like an egg fragment and will undergo disintegrative changes 

 similar to those of entire eggs, on being torn with the needle. If even 

 a small part of the original cortex is allowed to remain continuous 

 with the sphere it is fertilizable and the more cortical material present 

 the more will the sphere approach normal cleavage. 



It is significant that the fluid spheres which escape from the interior 

 of the mature unfertilized egg, whether nucleated or not, withstand 

 disintegration for a much longer period than do fragments, containing 

 cortical material, which have been produced simply by cutting an 

 egg into two or more pieces. 



It follows from these facts that the part of the starfish egg chiefly 

 concerned in development lies in its periphery. The interior when 

 separated from the cortex is incapable of developing. On the other 

 hand, an egg containing cortical material alone is able to carry on its 

 usual life activities. 



^ Chambers, R., Microdissection studies. I. The visible structure of cell proto- 

 plasm and death changes, Am. J. Physiol., 1917, xhii, 1. 



