THE GRRRN CRLLS OF CONVOLUTA IIOSCOPFRNSIS. 185 



otlier; in short, a series of stages are met witli — pairs of eqnnl 

 sized cells, pnirs in which one cell is of normal and the other 

 of reduced size, half normal, less than halP^ and even to a mere 

 speck (PI. 14, figs. 1C)A, B, c). 



This phenomenon we refer to again when dealing, at the 

 end of the section, with the systematic position of the infect- 

 ing organism. Tiie flagellated cells which settle down, with- 

 draw their flagella and surround themselves with a thick 

 mucilaginous wall do not necessarily pass through a period 

 of rest, nor do they necessarily divide up subsequently to 

 two or four green or colourless cells as described previously; 

 but the life-history is liable to be short-circuited in the 

 following manner : a green cell may encyst itself temporarily 

 and then cast off the cyst and escape once again as an active 

 cell. The organism under consideration exists also in a 

 colonial form (Palmella condition). The cells in the colony 

 form plates imbedded in mnsses of mucilnge produced by 

 the coalescence of the outer layers of the Avails of tlie indi- 

 vidu.'d cells. The cells in the colonial state are rounded, 

 uniforndy green, and possessed of a pyrenoid less refractive 

 than that of the active cell (figs. 14 and 15, PL 14). 'I'he 

 cells constituting the colony undei'go rapid division, being 

 rather budded off from the parent-cell than produced by 

 equal division of that cell. Hero and there among the mass 

 mature cells occur. lu these an eye-spot is visible, and the 

 pi-otopliist is differentiated into green chloroplast and colour- 

 less neck as in the active cells. The mature cell may be seen 

 moving inside its wall and every now and then escaping from 

 the wall as an active flagellated macrocyte. Hence, scattered 

 among the green cells of the colony are empty cysts consist- 

 ing of the walls left behind by escaped active cells (figs. 14 c 

 and 15, PI. 14). The green spherules from which we fii'st 

 obtained the infecting alga consist of such colonial stages 

 which have developed within, and come to fill completely, the 

 egg-capsule of Convoluta. Under other conditions the 

 colonial form is made np of cells which show the reticular 

 type of structure already described as occurring in resting- 



