326 



ROBERT CHAMBERS. 



starfish egg. In Fig. 9 the disintegration of the cytoplasm follow- 

 ing injury to the germinal vesicle has reached the surface of the 

 egg. The disintegrated area is quickly localized by a surface 

 film bounding a cup-shaped depression on the surface of the egg. 

 Roofing over the depression is the egg membrane. The egg 

 membrane can also be shown by cutting an egg in two by press- 

 ing the egg against the coverslip with the side of a needle. The 

 pressure of the needle cuts the egg in two without rupturing 

 the membrane, which, on releasing the egg, bridges the gap 

 between the pieces and holds them together (cf. Figs, n and 

 12, page 329). 



The difference between the consistency of the egg membrane in 

 the starfish and the sea-urchin egg is strikingly shown in the fol- 



11.36 



Fip. 8. Needle inserted at 11:36 A.M. through periphery of a sea-urchin 

 egg and left there. At 11:38 the cytoplasmic granules have been flowing 

 away from the needle. A new surface film begins to appear with the needle 

 left outside. At 1 1 145 the original egg membrane appears as a delicate 

 membrane partially lifted off the surface of the egg by the needle. 



FIG. 9. Lifting of a membrane from the surface of an immature starfish 

 egg following injury to the egg. a, local disintegration of cytoplasm following 

 destruction of the germinal vesicle (cf. Fig. 4). An egg membrane becomes 

 apparent as the cytoplasm retreats from it. b and c, gradual separation of 

 the membrane all over the surface of the egg. 



lowing experiments. With the eggs in a hanging drop the egg is 

 pressed against the coverslip with the side of a glass needle until 



