Volvox in South Africa. 551 



corresponding rays of the neighbouring cells (fig. 1, D, and Plate 

 XIII, B). 



With age, as the central protoplast becomes smaller and the 

 connecting strands grow finer, the star shape tends to disappear, the 

 protoplasts and connecting strands now appearing as a fine network 

 of which the protoplasts form the nodes (Plate XIX, D, E). 



Structure of the Protoplast. The protoplast consists of a very thin 

 limiting layer, the ectoplasm, a more or less massive chloroplast, 

 and an inner colourless endoplasm in which the nucleus lies and 

 which is continuous with the ectoplasm in the front of the cell this 

 colourless " throat " is on that side of the cell which faces towards 

 the anterior pole, or away from the posterior pole, i.e. on the ventral 

 side of the cell. 



In the endoplasm it is sometimes possible to distinguish a com- 

 paratively large vacuole containing one or more highly refractive 

 granules showing Brownian movement ; occasionally similar smaller 

 vacuoles may be seen in addition (fig. 1, A, D). These are not to be 

 confused with the contractile vacuoles, from which they are quite 

 distinct. Their content has not been tested, but they are probably 

 similar to the vacuoles described by Dangeard (1924, p. 1041) in the 

 case of V. globator. 



Each protoplast has a single large pyrenoid, protoplasmic strands 

 connecting it to its neighbours, two long cilia, and a varying number 

 of pulsating vacuoles, while in the anterior part of the colony each 

 contains a large red eyespot or stigma. 



Parts of the Protoplast (i) The Nucleus. In the somatic cell the 

 nucleus is small and inconspicuous. In healthy, fairly young coenobia 

 it is sometimes possible, by using a iVinch oil-immersion objective, to 

 make out the nucleus, or rather the nucleolus, in cells of the anterior 

 region. It lies in the colourless hollow portion formed by the 

 cup-shaped chloroplast. Treatment with iodine renders it clearer, 

 staining the nucleolus faintly yellow. In fixed and sectioned material 

 it is clearest when the material has been fixed in a dilute solution 

 of iodine in potassium-iodide, and subsequently hardened in dilute 

 chrome-acetic. In such preparations the nucleolus appears to be 

 composed of several small granules, staining much less deeply than 

 in the reproductive cells. At the best of times, however, in the 

 mature vegetative cell it is inconspicuous, and all nuclear study up 

 to the present has been done on the reproductive cells and the 

 products of their division. 



As compared with Janet's figures for V. globator (1912, fig. 6), the 



