184 F. KEEBLE ANM) F. W. GAMBLE. 



The restlng'-cells (PI. 14, figs. 11 and IG) \Mry considcM*- 

 ably ill form and in l)ehavionr. Thus, single flagellated cells 

 may come to rest, withdraw their flngella and, without form- 

 ing a thick wall, undergo longitudinal division into two or 

 four cells contained within the wall of the mother-cell. These 

 daughter-cells, at first without a distinct wall, organise 

 flagella, form a delicate cell-wall, and escape from the de- 

 liquescent mother-wall as active flagellated cells. Again, in 

 the case of the macrocytes, the active cell comes to rest, 

 surrounds itself with an extremely thick stratified wall, takes 

 on a spherical shape, and becomes green throughout as 

 though the whole cell were filled with small, polygonal, gi-een 

 granules. This appearance is due to the colourless proto- 

 plasm, which in the active stage is in large measure confined 

 to the cup-like hollow of the chloroplast, now radiating out 

 in all directions through the chloroplast to the outer wall and 

 so demarcating the green chloroplast into polygonal areas. 

 In these rounded resting-cells the pyrenoid is at first recog- 

 nisable, but later breaks up into a number of pieces, and 

 finally into many granules. The eye-spot may take the form 

 of a circular plate or I'ing lying near the periphery of the cell, 

 or it may disappear altogether. 



These rounded thick-walled cells (PI. 14, fig. 11), after a 

 period of rest, may organise four daughter-cells of oval shape 

 and having all the characters of the active cells except that 

 no pyrenoid is visible at first and no flagella are as yet 

 developed. A third form of resting-cell resembles that just 

 described, except for the fact that the green colour dis- 

 appears. lUiis colourless resting-cell appears, in surface view, 

 to be divided up into small, regular, polygonal areas, and in 

 this coll pyrenoid and eye-spot may be indistinguishable. 



Yet, again, paired resting-cells are met with. These con- 

 sist of two thick-walled cell-^, whose broad apposed surfaces 

 are flattened as by mutual pressure (IM. 14, fig. IG a). Such 

 paired cells are either green or colourless. Finally, yet 

 another form of resting stage occurs. In this the resting- 

 cells are paired, but one of the two cells is smaller than the 



