316 THALLOPHYTES 
toplasts of the other filament as shown in Figure 271. The 
protoplasts are unlike, for one migrates while the other does 
not. In behavior the migrating protoplasts may be regarded 
as sperms and the passive ones as eggs, although they show no 
differentiation in size or structure. Also, the filament which 
loses its protoplasts may be regarded as male and the receiving 
filament as a female individual. The zygospore builds about 
itself a heavy wall and at the end of a rest period develops 
directly into a new filament. 
Tt is now seen that the Conjugales stand quite apart from the 
previous groups in having no zodspores or swimming gametes, 
Fic. 272.—A species of Vaucheria (Vaucheria sessilis), showing the 
coenocytic habit of the filament, the odgonia at o, the antheridia at a, and the 
sperms escaping from un antheridium and entering an oédgonium ats. X 75. 
Partly drawn from nature and partly diagrammatic. 
and in having a peculiar kind of conjugation, in which entire 
protoplasts fuse and commonly reach each other through tubes. 
Although the gametes are alike in size and structure, they show 
some differentiation in the way they behave. The group is 
considered a highly specialized one. 
Tubular Algae (Siphonales). — These Algae, of which there are 
about 300 species, are so named because the plant body, no matter 
how long and thread-like, has no cross walls and, therefore, 
resembles a tube filled with protoplasm. The protoplasm con- 
tains many nuclei and many chloroplasts, and may be regarded 
as a much elongated multinucleate cell or as a filament with cross 
walls omitted. Such a plant body is called a coenocyte. The 
majority of the Siphonales are marine forms, iiving in warm seas, 
