336 ROBERT CHAMBERS. 



The endoplasmic 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, adheres tenaciously to glass. As long as it 

 possesses an intact surface it looks exactly like an egg frag- 

 ment and will undergo 1 disintegrative changes similar to those 

 of entire eggs on being torn with the needle (cf. Chambers, 



'!/-). 



The ability to produce endoplasmic spheres is possibly due to 

 the relatively tough egg membrane in the starfish egg which helps 

 to keep back the adherent cortex. In the sea-urchin egg, with an 

 extremely delicate egg membrane, it has been impossible to cause 

 the interior to flow out, as the cortex tends to flow with it. 



The sand-dollar egg behaves very much like the starfish egg. 

 The egg membrane is appreciable in the unfertilized egg and endo- 

 plasmic spheres are readily produced. 



A difference in the functional activities of the cortex and inte- 

 rior of the starfish egg is discussed under the headings 6 and 7. 



5. THE HYALINE PLASMA LAYER. 



Prior to fertilization the cytoplasmic granules in the sea-urchin 

 and sand-dollar egg lie close to the surface. Within ten minutes 

 after fertilization the granules have undergone a centripetal migra- 

 tion, leaving an appreciable peripheral zone of a hyaline appearance 

 which has been called the hyaline plasma layer (Loeb's gelatinous 

 film, '13, p. 19). 



The microdissection needle indicates that this layer is relatively 

 firm and gelatinous. The very fluid internal cytoplasm may be 

 made to flow out through a rupture in this layer if the egg be torn. 

 This is shown in Fig. 19. The cytoplasmic granules lie against the 

 inner boundary of this layer and may be seen oozing out through 

 the small tear in this layer and through a tear in the fertilization 

 membrane to the exterior. 



The hyaline plasma layer adheres very tenaciously to the needle 

 and when an egg has been deprived of its fertilization membrane 

 the egg sticks to everything it touches. 



Loeb has called attention to the fact that the hyaline plasma 



