iv] GREEN CELLS OF CONVOLUTA 105 



Or, to pursue another line of argument. The 

 Zoochlorellas of some animals are typically plant-like 

 cells. They possess a chloroplast, a nucleus and a 

 cellulose cell-wall. But in other animals, in C. ros- 

 coffensis, for example, the green bodies are of simpler 

 build. Each consists of a naked protoplast which is 

 made up of a green chloroplast and a colourless mass 

 of eccentrically lying protoplasm in which a nucleus 

 may be included (Fig. 17, p. 85). The green tissue, 

 composed of vast numbers of these elements, appears 

 to be as much a part of the animal as any other of its 

 tissues. So much is this the case that all attempts to 

 cultivate the green cells of C. roscoffensis outside the 

 body end in failure. They are no more capable of inde- 

 pendent existence than are the chloroplasts of the 

 chlorophyllotis tissues of a green plant. 



What is there to prevent us from assuming, as 

 Haberlandt has assumed, that the green cells of C. 

 roscoffensis are not complete cells but merely chloro- 

 plasts, and that, like the chloroplasts of the green plant, 

 they are transmitted as colourless particles (leuco- 

 plasts) from the organism to its eggs, and, multiplying 

 as the egg divides to form the embryo, reappear as 

 green chloroplasts in the tissues of the new genera- 

 tion ? On this hypothesis the colourless part of the 

 green cell of C. roscoifensis (Fig. 17) is an animal cell 

 which attends upon the green chloroplast. In other 

 words, just as a green cell of a flowering plant 



