THALLOPIIYTES 



*3 



or of gametes, by using various nutrient media. Tne 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. — Hydrodidyon: a 

 completed young net within its 

 mother cell. — After Klebs. 



Figs. 48-52. — Hydrodidyon : 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. — Hydrodidyon: 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 



