THE GREEN CELLS OF CONVOLUTA ROSCOFFENSIS. 193 



The infecting organism, though without Hagelhi, now 

 resembles in other respects the active flagelkited free stage. 

 It is, in fact, as both its histoh^gical features and its devek)])- 

 ment show, a daughter-cell produced by tlie division of a 

 colourless resting-cell. Sucli resting-cells on resuming 

 activity undergo division into four (the paired cells into as 

 many as eight) daughter-cells, which, as described in Section 

 IV, are discharged together or severally through a circular 

 opening in the thick mucilaginous wall of the cyst. Sub- 

 sequently these cells surround themselves, in the free state, 

 each with a thin wall. In the body of Convoluta the forma- 

 tion of a definite wall is suppressed. 



The small culourless or faintly yellow cell, which is often 

 the first recognisable sign of infection, is a daughter-cell 

 which has been produced outside the body of the animal 

 by the division of such a resting-cell as that just desci'ibed. 

 Convoluta is then infected normally either by a resting-cell 

 or by non-motile daughter-cells produced by the division of 

 a resting-cell, though, as already shown, the organism in its 

 flagellated phase may be taken up and give rise to normal 

 infection. 



We have now traced the infecting organism to its place in 

 the body of Convoluta. At certain, fairly constant, stations 

 of the body, several naked green cells lie, each in a clear 

 vacuole. At about this stage, or after their further division, 

 the green cells lose their regular oval outline, and the colour- 

 less part of the protoplast becomes more or less excentrically 

 placed with respect to the chloroplast. It is easy to cause 

 free active cells to uuderi>'o similar changes. All that is 

 necessary to effect this is to transfer them from sea-water to 

 a fluid — e. g. diluted sea-water — of lower osmotic pressure. 



Hence we infer that the peculiar and variable shapes of the 

 green cells of adult Convolutas are due to the osmotic pressure 

 of the vacuolar fluid in which they lie being lower than that 

 of sea-water. Incidentally, this observation serves to clear 

 up another point, liaberlandt makes the suggestion that the 

 colourless, excentrically-lying part of the green cell is in 



