THE GREEN CELLS OF CONVOLUTA KOSCOFFENSIS. 203 



have sliowu, require considerable modification, led liim to 

 conclude that the animal relies on the green cells for its 

 food supply. 



Georgevitsch (1899), findiug that colourless larvas die, if 

 uninfected, within two or three days, seemed thereby to 

 establish the existence of a yet closer dependence of animal 

 on green cell. 



We have shown in a former paper that von Graff^s state- 

 ment is too absolute, and that of Georgevitsch inaccurate. 



We may summarise our own observations as to the ingestion 

 of food by Convoluta. 



A well-marked mouth — already described by von Graff in 

 adult animals — is present in just hatched animals. This 

 mouth, capable of a wide gape, is situated on the under 

 surface, about the middle of the body. When open the mouth 

 is connected by a short, ciliated, ectodermal invagination 

 with an axial mass of highly vacuolated tissue which con- 

 stitutes a rudimentary gut. 



By means of this mouth a young Convoluta takes up ahnost 

 any objects which it can encompass ; diatoms and unicellular 

 green algaj form the staple diet in the open, while in the 

 laboratory starch-grains, litmus, lamp-black, and sand-grains 

 may be swalloAved. 



If colourless uninfected Convolntas are cultivated in water 

 devoid of the infecting alga but rich in other organisms, such 

 as diatoms, they continue to feed actively for some time — for 

 a week or more. But after this period they become increas- 

 ingly inert and ultimately cease altogether to take up food. 



In this state they await, as it were, the infecting alga. If 

 the latter is supplied they ingest it, and, as it develops, the 

 animals resume their activity. If, on the other hand, the 

 infecting organism is still withheld, the lethargic condition 

 becomes more pronounced, and undergoing gradual diminu- 

 tion in size, Convoluta finally dies though lying in the midst 

 of food of a kind which, at an earlier stage, it took up and 

 digested readily enough, and on which young infected Con- 

 volntas are still feeding. It is to this remarkable behaviour 



