Aiembrane Formation 369 



V. LOSS OF PIGMENT IN ARBACIA EGGS 



Since the pigment of Arbacia eggs is soluble in water it follows 

 that the membrane of the chromatophore granules must be imper- 

 meable to the contained pigment, otherwise it would diffuse 

 through the cytoplasm and out of the eggs (providing the egg 

 membrane were also permeable to it). If the eggs are heated 

 diffusion of the pigment into the sea-water takes place, showing 

 an increase in permeability in both the chromatophore and 

 plasma membranes. I have never noticed a permeability (to pig- 

 ment) of the former independent of the latter. There is also 

 evidence that the impermeability of the granule membrane is 

 dependent on the plasma membrane. If unfertilized eggs are 

 crushed slightly under a cover glass, part of their contents will 

 flow out into the sea-water and round up. The colored granules 

 which have been pressed out immediately lose their pigment 

 while those within the original fraction still retain it. I do not 

 think this can be due to crushing because the bodies are so small. 

 There is also a difference in the optical properties of the surface 

 newly formed about the extruded protoplasm as compared with 

 the old. 



The same phenomenon is observed when eggs are placed in 

 hypotonic sea-water (sea-water one third, distilled water two- 

 thirds. The eggs swell and their surface layer becomes indis- 

 tinct. 



When this occurs the pigment immediately disappears from 

 granules and diffuses throughout the cytoplasm. At the same 

 time in many eggs a thin irregular membrane separates. 



A loss of the pigment, which becomes a yellow-red color, occurs 

 in four times concentrated (by evaporation) sea-water^^ The 

 same solution occurs in CH3COOH in concentrations greater than 

 those required to produce membranes. This index of determin- 

 ing permeability changes has been used by Lillie^" working on 

 muscle cells. Pure isotonic solutions of electrolytes which cause 



"See Loeb's description of this in Strongylocentrotus U. Calif. Pub. Physiol, ii, pp. 73-fii, 1905. 

 2" Lillie, R.: Am. Journ. Physiol, xxiv, p. 14, 1909, and id. p. 459. 



