CH. v] NATURE OF PL ANT- ANIMALS 131 



The attempts have also provided us with informa- 

 tion with respect to the full significance of the 

 association. In order to make clear the nature of 

 this information, we will first consider very briefly 

 the normal course of events in the development of 

 C. roscoifensis in ordinary sea-water containing the 

 infecting organism and then its behaviour in filtered 

 sea-water which contains no infecting organisms. 



Within a day or two of hatching, C. roscoffensis, 

 maintained in ordinary sea-water, is found to have 

 become infected. The colourless cell, the first sign of 

 infection, divides and the colourless daughter cells are 

 sown about the body. They become green, divide and 

 re-divide till ultimately the many thousands of algal 

 cells making up the green tissues of the organism, lie 

 in dense masses in the body. For a time, the animal 

 continues to feed : but, after a while, it abstains from 

 ingesting solid food and lives a simple, easy life, fed by 

 the products of the photosynthetic activity of its green 

 cells. Later on, unsatisfied with the amount or kind 

 of tribute which it thus receives, the animal begins to 

 digest its algal cells and may continue the habit until 

 the green tissue has, in larger measure, disappeared. 

 In the meantime, however, C. roscoffensis has matured 

 and produced eggs, the substance of which has been 

 supplied by the green cells ; so, even though it now 

 dies as the consequence of its ill-considered greedi- 

 ness, the continuance of the species is assured. 



92 



