548 



Annals of the South African Museum. 



2. (7eH Membranes. The cell membranes can usually be seen in 

 living, unstained material ; sometimes, however, they do not show 

 clearly, and careful focussing is always necessary. If a drop of a 

 dilute aqueous solution of methylene blue is run in, the membranes 

 show up very distinctly ; in living material, if the solution is 

 sufficiently dilute, the colonies continue moving for some time, and 

 the action of the cilia can be followed. The protoplasts with their 

 connecting strands stain blue, the limiting membranes clear, rather 

 deep purple, the " gelatinous " wall between the protoplast and the 

 limiting membranes very faint purple. This method works equally 

 well in living or preserved material. 



The outer cell membranes are united to form a common wall to the 

 whole spheroid ; this is somewhat thickened and is mucilaginous on 

 the outside. In large mature colonies it generally forms a continuous 

 curve (Plate XV, B), but sometimes, particularly in smaller colonies, 

 the component curves formed by the slight convexity of each cell 

 wall may be distinguished. In the inner membrane, distant usually 

 about 22 ju, (18 to 24 p.) from and concentric with the outer membrane, 

 the corresponding curves are usually more clearly marked ; it is 

 slightly thinner than the outer membrane (Plate XV, A). 



Within the inner membrane, and occupying by far the greater 

 part of the spheroid, is a hollow filled with a mucilaginous liquid. 

 When stained with Delafield's haematoxylin, gentian violet, safranin, 

 or methylene blue this fluid appears as an irregular network of 

 coloured strands, the meshes remaining unstained (cf. PI. XLI, I). 

 No trace was seen in either living colonies or prepared sections of 

 any regular radial arrangement of strands such as Janet (1912, pp. 

 35-37, figs. 1 and 2) describes and figures for V. globator. 



