66 SEAWEEDS 
The Geographical Distribution of the Dictyotacee: 
is characteristic of temperate and tropical seas, but 
reaches its maximum in the warmer waters of the 
tropics. 
TILOPTERIDACE. 
General Characters—This small order is of uncer- 
tain position, since the true character of the repro- 
ductive organs has not yet been ascertained. These 
are of two sorts: (1) bodies comparable with the 
antheridia of the Cutleriacew ; (2) larger unilocular 
bodies, presumptive oospheres. No process of fer- 
tilisation has been observed, and the thallus affords 
from its morphological character no other clue than 
the indication of strong agreement with the L£cto- 
carpacec. 
The Thallus in all three genera—viz. Tilopteris, 
Haplospora, and Scaphospora—takes the form of tufts 
of more or less branching filaments attached to the 
substratum by root-hairs. In Zilopteris the branches 
are opposite, and the primary branches bear short 
secondary ones; while in Haplospora and Scaphospora 
the branches are alternate butirregular. The upper 
portion of each filament always consists of a single 
row of cells, while the lower consists of tiers of 
several cells of equal length. Growth in length 
takes place by intercalary division. The upper ends 
of the branches are fine and hair-like, the cells 
becoming longer, and containing little protoplasm 
and few chromatophores. The cells contain each a 
large central nucleus with nucleolus, surrounded by 
