FRESH-WATER ALG, 205 
where they are found. These balls float freely at 
a small depth in the water, and are often washed 
ashore by the waves, where they accumulate in 
dense masses, and are again covered over with a 
parasitic confervoid growth: 
In ditches by the waysides, may often be seen 
large dark-green intensely slimy masses of rigid 
filaments as thick as horse hair. This belongs to 
the genus Zygnema (Fig. 18), one of the largest and 
most curious divisions of the conferve. Under 
Fic. 18.—ZYGNEMA DECIMINUM. 
the microscope, the filaments are found joined 
parallel to each other by transverse tubes, and 
marked by articulations longer than broad. They 
are remarkable for exhibiting more distinctly than 
in the other conferve the process, already alluded 
to, of conjugation or inosculation of neighbouring 
filaments, in order to the production of the rest- 
ing-spores. They are also distinguished for the 
spiral arrangement of their internal granular mat- 
ter, which, in some cases, is like a continued multi- 
