132 PLANT-ANIMALS [CH. 



C. paradoxa exhibits a like behaviour. Though it 

 never becomes a total abstainer from ingested, solid 

 food, there are times when it makes inroads upon its 

 yellow-brown cells, and indeed, if supplies of solid 

 food are withheld from it, C. paradoxa exhibits no less 

 scruple than C. roscoffensis in raiding its algal cells. 



But if C. roscoffensis is maintained in filtered sea- 

 Avater, and hence prevented from becoming infected 

 with its green algal associate, the course of events is 

 very different. Even though diatoms and other micro- 

 organisms are added to the filtered sea-water, C. ros- 

 coffensis, after a few days of active feeding, ceases from 

 ingesting solid food-substances. For a while, the fat 

 and other reserve food-substances contained in its body 

 suffice for the needs of the animal, but, when these 

 reserves are exhausted, starvation begins. In spite 

 of the addition of food-material to the filtered sea- 

 water food-material which its infected green fellows 

 are enjoying uninfected C. roscoffensis abstains 

 obstinately from ingesting it. It is waiting for the 

 development of its green tissues which ought by this 

 time to have been laid down in the body. Thus 

 it waits, and starves, dwindles till it becomes in- 

 visible to the eye, and, ultimately, after weeks of 

 waiting, dies. If, before this happens, the algal in- 

 fecting organism is added to the water, the animal 

 may should exhaustion be not too pronounced- 

 ingest it. Having thus achieved infection, it is a 



