Hazen: Lire HISTORY oF SPHAERELLA LACUSTRIS 218 
companied by a constant rotation on the longer axis, from right 
to left, so that the path described is a spiral. The cellulose invest- 
ment of the zooid, which was at first indistinct or invisible, soon 
becomes separated from the colored contents by an accumulation 
of water and appears as a delicate colorless bounding line (Fig. 6). 
Sometime later under favorable circumstances this cell-wall be- 
comes still further distended and very delicate strands of proto- 
plasm may be seen radiating from the colored mass to the cell- 
wall (Fig. 7). 
Meanwhile a border of yellowish-green chlorophyl has been 
forming about the zooid replacing the outer part of the haemato- 
chrom. After a longer or shorter period of movement the zooids 
come to rest, usually adhering to some object by their cilia at first ; 
the radial protoplasmic strands and cilia disappear, but often at the 
anterior end the sheaths which rigidly supported the bases of cilia 
remain, connecting the cell-wall with the protoplasmic body (Fig. 8). 
This quiescent cell may quickly divide again. The process, how- 
ever, differs slightly from that of the original division as no ap- 
preciable distention of the mother-cell-wall occurs (Fig. 9); 
furthermore, the daughter-cells early develop cilia and move about 
within tlie mother cell-wall, often for half an hour or longer before 
going out ; thé daughter-cell-walls, also, are more likely to be well 
developed than those of the first generation. These zooids after 
breaking out increase in size forming more chlorophyl from the 
periphery inward like those of the first generation (Fig. 10). 
They also may arrive at a brief quiescent condition and repeat the 
process of division by which they were themselves formed (Figs. 
II—I4). 
The time elapsing between these divisions is variable; some- 
times the second generation is produced on the same morning as 
the first, but more frequently it appears that new generations are 
formed on successive mornings. How long this frequent division 
may continue has not been determined, but the colony may re- 
main in the motile condition for three or four weeks. 
At any point in the cycle, cells may go into a permanent resting 
stage. In that case, after the cessation of movement and disap- 
pearance of the protoplasmic processes (Fig. 16), a new thick cel- 
lulose coat is secreted close about the protoplasmic body (Fig. 17), 
