550 Annals of the South African Museum. 



Occasionally in older colonies the central mucilage may become 

 yellowish brown in colour. The inner membrane then shows very 

 clearly even under low powers of magnification (Plate XXXVIII, A). 

 A similar discoloration in senile colonies of F. globator was noticed 

 by Klein (1889, p. 157) and ascribed by him to bacteria. In some 

 but not all the colonies showing this discoloration in F. Rousseletii 

 bacteria were seen ; the discoloration of the mucilage would appear 

 not to be caused entirely by bacterial action. 



In surface view, or cut tangentially, the cell prisms are polygonal 

 in outline, most often hexagonal, but occasionally pentagonal or 

 heptagonal. They appear in living unstained material of F. capensis 

 in Plate XXXVIII, D ; fig. G on the same plate shows the mem- 

 branes stained with Delafield's haematoxylin. This photo is part of 

 a mature asexual colony, showing the pore above a daughter colony 

 which had been removed by the pressure of the cover-slip. It illus- 

 trates the fact that, unless previously carefully fixed, the protoplasmic 

 strands may be withdrawn before the stain takes effect. 



3. Protoplast. Not only the size, but also the shape, of the proto- 

 plast depends on the age of the cell and its position in the coenobium. 

 Before birth it is oblong in side view, its apex nearly reaching the 

 outer membrane, and polygonal in surface view owing to mutual 

 pressure (Plate XXXIX, A, B). After birth, as the colony matures, 

 the shape of the protoplast changes. Near the anterior pole it 

 remains ovoid or becomes broadly pear-shaped in side view, while 

 elsewhere in the colony it becomes markedly pear-shaped with broad 

 basal portion and more or less attenuated apical outer half (fig. 1, 

 A, B). In mature colonies the cells near the posterior pole are often 

 very characteristic above the broad basal part the protoplast 

 narrows to form a neck, then at the apex suddenly widens again to 

 form a structure like the head of the hammer-head shark, the cilia 

 being inserted at the two ends of the hammer (fig. 1, C). 



After birth, the protoplast of the somatic cell continues to in- 

 crease in size for some time. After a while, however, about the time 

 that the reproductive cells begin to divide, enlargement ceases, the 

 protoplasts for a time remain the same size, then, as the colony 

 begins to mature, the protoplasts slowly dwindle, particularly in the 

 posterior region. 



In surface view in a middle-aged colony the protoplasts appear 

 star-shaped, the rays being formed by the relatively broad proto- 

 plasmic connections. The points of the rays reach the centres of 

 the sides of the polygonal membrane, there meeting and fusing with 



