STRUCTURE OF PROTOPLASM. 3 13 



thick. Notwithstanding the possession of a heavier wall these 

 eggs can be dissected with as much ease, ending in the same re- 

 sults as those less mature ova having but a thin pellicle as cover- 

 ing. Droplets can be pinched off, the eggs torn from within 

 outwards, or rapidly severed by a needle, without any indication 

 of escaping protoplasm. The severed parts in every case in- 

 stantly round up into droplets with walls apparently identical 

 with the parent wall. This capacity to form a wall instantly at a 

 ruptured point through conversion of the cytoplasm into a 

 semi-rigid gel is not influenced by relatively great changes in the 

 concentration of the surrounding medium, for it is as pronounced 

 in very saline water as in normal sea-water. 



There is no evidence of miscibility on the part of the proto- 

 plasm. 



Fully Mature Ova. 



The protoplasm of mature, normally discharged eggs is de- 

 cidedly viscous, noticeably more so than that of well-developed 

 unripe eggs. Thus has the highest degree of viscosity been 

 reached in the development of the ovum, the transition taking 

 place during the last periods of growth. 



The wall likewise has undergone a marked change and become 

 a hyaline, rigid gel, 0.8-1.2 microns thick, still very pliable and 

 extensile, slightly contractile and exceedingly adhesive. 



The wall of the mature normal Fucus ovum is capable of con- 

 stant repair and this capacity often persists to the very last in a 

 dying egg. Not until gelation of the protoplasm is well advanced 

 does a rupture of the wall fail to be closed by a rapid conversion 

 of the plasma matrix into a rigid gel. The capacity for wall 

 formation is, then, one of the last essential properties of the living 

 substance to be lost. 



In all stages of its development before its normal discharge 

 the egg shows no injury in consequence of dissection. The 

 mature egg, on the contrary, is very sensitive to dissection, 

 although its behavior is extremely variable. Every precaution 

 was taken to prevent a misinterpretation of results due to obser- 

 vation of degenerated protoplasm. Such precaution was found 

 to be more necessary with the ova of plants than with those of 

 animals. To determine that the ripe eggs used for dissection 



