THALLOPHYTES 
or of gametes, by using various nutrient media. The zygospore is a 
heavy-walled resting cell that settles to the bottom of the water and 
resembles a Pleurococcus cell. After a more 
or less prolonged resting period, the zygo- 
spore produces two or four large biciliate 
zoospores, which escape into the water (figs. 
FIG. 47. Hydrodictyon: a 
completed young net within its 
mother cell. After KLEBS. 
FIGS. 48-52. Hydrodictyon: 48, gamete; 
49, gametes fusing; 50, zygospore; 51, four zoo- 
spores developed by the zygospore; 52, zoospore 
escaped from zygospore. 48-50, after KLEBS ; 
51, 52, after PRINGSHEIM. 
51, 52) and develop into large, irregular, many-angled, thick-walled 
cells (polyhedra), which persist through the winter (fig. 53). Upon the 
FIGS. 53, 54. Hydrodictyon: 53, polyhedron formed by a zoospore; 54, young 
net forming within a polyhedron. After PRINGSHEIM. 
return of favorable conditions, each of these polyhedra (resting cells) 
forms internally a small net of 200 to 300 cells (fig. 54), which escapes, 
and the multiplication of nets is begun. It is a noteworthy fact that 
