m] GREEN CELLS OF CONVOLUTA 95 



upwards of a month in filtered water ; that is, under 

 conditions, in which it is deprived of all external 

 supplies of food. When subjected for long periods 

 to these conditions, the animals become reduced in 

 size and as is the case to a yet more marked degree 

 with those kept in darkness also show an extra- 

 ordinary reduction both in number and size of their 

 yellow-brown cells. 



In prolonged darkness, the yellow-brown cells, once 

 their reserves of food-material have been extracted 

 from them to meet the needs of the animal, are 

 digested wholesale by C. paradoxa. If the water in 

 which they are contained is altogether devoid of food 

 supplies, the attack by the animal on its coloured 

 cells occurs all the sooner. Even in the light, if 

 external food supplies are withheld from C. para- 

 doxa, a time comes when, although the yellow-brown 

 cells are supplying it with photosynthesised food- 

 materials as fast as they can under the difficult 

 circumstances, it turns upon them ; killing and 

 digesting the goose which laid its golden eggs. 



Microscopic examination of animals kept in pro- 

 longed darkness supplies evidence that the degenera- 

 tion of the yellow-brown cells is not a mere decay 

 within the body, but is the result of a true process 

 of digestion exerted on them by the animal. The 

 first sign of digestive action is a reduction in size 

 of the yellow-brown cells. They assume a more 



