
Fie. 349. Cosmarium and Anthrodesmus 
Desmids reproduce sexually by the conjugation of two cells (the walls of each 
separate into two parts; the contents escape and fuse to form a zygospore, which 
surrounds itself with a thick wall); asexually by division of one cell into two 
across the narrow part or isthmus, each half growing out a new half. Left: 
above, mature individual of Cosmarium (x 1150); below, a zygospore (x 700). 
Center : a stage in asexual reproduction of Cosmarium. Right: three successive 
stages in asexual reproduction of Anthrodesmus (x 1090). See Fig. 348 
Sm 
Gtr 
oo 
oT 

Fig. 350. Forms of diatoms 
Diatoms are alge which are brown and have siliceous shells. Reproduction is 
* similar to that of desmids (see Figs. 348 and 349). Diatoms are very abundant 
in both fresh and salt water. Many cleansing preparations owe their efficacy to 
the scouring action of the siliceous shells of diatoms. (x 225) 
