44 THE ROYAL SOCIETY OF CANADA 



The cell nucleus is an optically hyaline sphere occupying about 

 one-fourth of the cell. Within the hyaline substance of the nucleus 

 lies a small body, the nucleolus, which is visible because of its high 

 refractivity. 



The extremely sensitive nature of the nucleus is evidenced by the 

 fact that, on the slightest mechanical injury, certain changes occur 

 which cause the nucleolus to fade completely from view. The nucleus 

 may be pushed about in the cell without apparent injury. If the 

 surface be torn the contents flow out and the nucleus disappears. 

 If care be taken the nucleus may be cut in two, each portion at once 

 assuming the shape of a sphere. This indicates a high power of 

 extensibility and regeneration in the surface film. On pulling the 

 nucleus out of the cell the nucleus immediately begins to swell and 

 fades from view. 



The Egg Cell of the Flounder. The immature egg of the flounder 

 of about half a millimeter or less in diameter was selected for this 

 study. The nucleus is a liquid sphere similar to that of the nerve cell. 

 It, however, possesses a more persistent surface film or nuclear mem- 

 brane. This may be caught by the tip of the needle and a consider- 

 able strand pulled out. The nucleus is easily cut into several pieces 

 which immediately round Up. On touching one another the portions 

 fuse indicating the absence of a morphologically persistent nuclear 

 membrane. 



Considerable injury is necessary to bring about dissolution of 

 the nucleus and the surface film is the last to disappear. Injury 

 apparently causes this film to set into a definite membrane, so that 

 when torn it often wrinkles and a fluid (apparently the nuclear sap) 

 collects between the cytoplasm and the partially collapsed membrane. 



The flounder egg is surrounded by a closely fitting tough egg 

 membrane. This rather interferes with an adequate comprehension 

 of the consistency of the cytoplasm, especially of that on the cell 

 surface. Results obtained from studies made in other marine ova 

 are more satisfactory. 



The egg cell of Asterias. Work done at St. Andrews on Asterias 

 confirms the views already published (Chambers '17'', 17^) on the cell 

 protoplasm of Echinoderm ova. The protoplasm consists of a hya- 

 line fluid matrix in which are imbedded granules of various sizes. 

 The fluid offers no perceptible resistance to the needle and an indica- 

 tion of its very slight viscosity lies in the fact that, when the needle is 

 moved through the fluid, the only granules displaced are those in the 

 immediate vicinity of the needle. The protoplasm coagulates with 

 ease. Mere compression will sometimes cause an egg to coagulate into 

 a solid mass. 



