THE PERMEABILITY OF CELLS 



523 



Fig. 1 Diagram of the areas which may be distinguished in a centrif uged Para- 

 moecium, (electric centrifuge 1.5 hours at a radius of 6 cm.) stained in neutral 

 red. 



O, oil (?) globules; V, food vacuoles, the contained matter often red stained; 

 S, granules stained in neutral red; N, macronucleus; C, crystals. If the organism 

 is uninjured, there is a very rapid redistribution of substances in the protoplasmic 

 circulation. 



Figs. 2 and 3 Diagrams of the distribution of substances in centrifuged Chae- 

 topterus (2) and Arbacia (3) eggs stained in neutral red. Elongation in the axis 

 of the force has taken place. O, Oi, O2, oil globules; in Chaetopterus of two 

 sizes and of two densities Oi and O2; N, nucleus; C, clear area; in Chaetopterus 

 containing a few scattered yolk and minute red stained granules; in Arbacia 

 containing at the surface a few pigment bodies (chro matophores) and numerous 

 minute stained granules, quite unmoved by the cent rifuge. At the time of fer- 

 tilization these disappear, apparently going to form the substance which passes 

 out of the egg and hardens to a fertilization membrane. Y, yolk; in Chaetopterus 

 appearing pink from numerous minute red stained granules most of which col- 

 lect in a mass (S) just under the oil. P, the pigment granules, appearing dark 

 red from absorption of the neutral red dye. 



