130 Papers from the Marine Biological Laboratory at Tortugas. 



Whereas this supposed significance of permeability has not been proven, 

 the sea-urchin's egg is not an exception. Spores, eggs, seeds, and pupae are 

 usually inclosed in relatively impermeable membranes. A striking example 

 is the cocoa nut. Whereas an active organism may be partly inclosed in a 

 relatively impermeable skin, great activity is always associated with a rapid 

 interchange with the medium, and this is possible through more permeable 

 portions (lungs, gills, kidneys, gut). 



The relation of permeability to oxidation can hardly be determined 

 until more is known about the mechanism of animal oxidations. These seem 

 to depend on structure since complete oxidations cease when structure is 

 completely destroyed. Reference is made only to oxidations resulting in the 

 formation of CO. 2 Oxidizing enzymes such as tyrosinase, which are inde- 

 pendent of structure, do not completely oxidize the substances acted on. 



