SPH^RELLA 



181 



hair-like cilia, whose incessant whipping of the water carries the 

 organism along. There is also a red pigment spot at the ciliated 

 end of the cell (Fig. 176, -4, _p). This free-swimming, ciliated 

 cell is of a type strikingly different from Pleurococciis, but it 

 is believed to represent very nearly the ancestral condition of 

 many groups of algae. 



Sphcerella lacustris (Hccmatococcus pluvialis) is found freely 

 swimming in rock pools and sometimes in troughs and basins, 



FIG. 176. Sphvsrella 



A, n, Sphwrella lacustris: a single cell in detail and a group of daughter proto- 

 plasts within the parent cell. (.', /.', Sphxrella Butschlii: numerous small sex- 

 ual elements or gametes are shown in the parent cell C, and I) illustrates their 

 fusion in pairs to give the sexually formed cell or zygospore z. fi, after 

 Scheuck ; C, D, after Blochmaim 



I 



and is frequently so abundant as to color the water a bright 

 green. The organism multiplies very rapidly, for the larger indi- 

 viduals (Fig. 176, A) form 2-16 daughter cells (Fig. 176, B), 

 which escape from the mother-cell membrane, swim away, and 

 after a period of growth form in their turn a new set of 

 daughter cells. The free-swimming cells come to rest at times, 

 becoming thick-walled resting cells, which are colored red by 

 a peculiar pigment. These resting cells carry the plant over 



