556 Annals of the South African Museum. 



Mast (1923, 1927, etc.) has studied the structure and function of 

 the eyespot in great detail. He finds that it is essentially similar 

 throughout the Volvocales, reaching its highest development in Volvox, 

 where the light is received by a hyaline lens situated in the hollow of 

 the cup-shaped red structure, i.e. on the dorsal side of the cell, and 

 that the yellow and red rays are transmitted through the eyespot into 

 the cell, while the green and blue rays are reflected, the resultant 

 bluish-green ray being distinguishable in certain circumstances 

 (1927, p. 206). The stigma directly controls the action of the cilia. 



(vi) Protoplasmic Connections. The protoplasmic connections be- 

 tween adjacent cells probably originate in the incomplete division 

 of the cytoplasm during the division of the gonidium while the 

 greater part of the cytoplasm rounds of? round each daughter nucleus, 

 bridges of cytoplasm remain between neighbouring cells. In the 

 two species here in question these " bridges " persist throughout the 

 life of the coenobium. 



In fairly young colonies the protoplasmic connecting strands are 

 comparatively thick and distinct ; their appearance depends to some 

 extent on the age of the colony and on external conditions. In 

 colonies before and immediately after birth the connections are diffi- 

 cult to see and are merely very small, thread-like bridges between 

 adjacent cells (cf. fig. 1, G). After birth, as the protoplasts separate 

 from one another, they get drawn out, and in a typical young middle- 

 aged colony, i.e. one in which the gonidia are still in the stage of 

 division (PI. XIII, B) or, if sexual, where the oospheres are about 

 ready for fertilisation or the sperm bundles beginning to form, the 

 protoplasmic connections are best seen by examining living indivi- 

 duals under a low power against a black background. Since the 

 chloroplast extends into the protoplasmic connections, the whole 

 network is a vivid green colour, the denser protoplasts forming the 

 nodes of the net, the protoplasmic connections the green sides of the 

 mesh. 



Examined under higher powers, the strands are seen to be, in part 

 at least, tapering elongations of the broad basal part of the proto- 

 plast, broad at their commencement, where contractile vacuoles 

 often occur, dipping slightly downwards and becoming narrowest 

 where they reach the dividing membrane; there is usually a slight 

 thickening at the junction of the two strands, i.e. where they pass 

 through the wall. Whether this is actually a thickening of the 

 strand or, more probably, due to the structure of the wall, was 

 doubtful. Not infrequently a contractile vacuole occurs in the 



