EXPERIMENTAL STUDY OF THE SEA URCHIN EGG 



31 



HYALINE PROTOPLASM 



Fig. 12. A sea urchin egg after exposure to centrifugal force becomes strati- 

 fied into layers of granules and clear protoplasm. C, C t gives the direction of 

 the applied centrifugal force. The embryo which develops from the centrifuged 

 egg (right) is normal except for pigmentation. The polarity of the egg has 

 not been altered by centrifugation. 



clear protoplasm without any microscopically visible particles in it, called 

 the hyaline protoplasm. 



Thus we have a means of shifting all the microscopically visible con- 

 stituents of the egg and of moving them away from their original positions. 

 If any of these constitutents — the fat droplets, the pigment granules, or this 

 second type of unpigmented granules — are responsible for the organization 

 of the egg, then a completely distorted larva should result. As a matter of 

 fact, the strongly centrifuged egg develops into a perfectly normal larva 

 when fertilized. Figure 12 shows one of these larvae. Other larvae may show 

 a shift in the position of the pigment. It may all be concentrated at one end 

 of the larva; or on the side of the larva, so that one side is pigmented and 

 the other is not. But the larvae are perfectly normal in all essential respects. 



More than that, it has been found that if the egg is exposed to very high 

 centrifugal forces in an ultracentrifuge, the egg becomes torn apart so that 

 its components are separated as cream is separated from milk, and parts 

 of the egg almost entirely free of granules are obtained. These parts of the 

 egg, practically free of any microscopically visible granules, may develop 

 into perfect larvae. Therefore, none of the microscopically visible com- 

 ponents of the endoplasm of the egg can have anything to do with its 

 organization. And thus we must conclude that the organization depends 

 upon some of the finer structure of protoplasm which is not disturbed by 

 the centrifuging. 



