CUBAN SEAWEEDS. 205 
Nearly allied to Caulerpa, are Halimeda and Udotea, which are 
composed, not as in Caulerpa, of a single cell, but of several sim- 
ilar cells packed together into a frond. These genera would 
hardly be called plants at all by the Fig. 54. 
common observer, as they are coated 
with carbonate of lime and resemble 
corals. In fact, they are corallines or 
algee with a calcareous covering. In 
some species this coating surrounds 
ach filament separately, in others it 
surrounds the collective mass of fila- 
mentous cells of which the plant is 
composed. Referring to these plants, 
Cuvier wrote, ‘il existe dans la mer 
des corps assez semblables aux poly- 
piers par leur substance et leur forme 
générale aù lon n’a pu encore aper- 
cevoir les polypes.” Lamouroux, how- 
ever, went farther, and described the 
polyps which, it is needless to say, existed only in his own imag- 
ination. At present, there is no doubt of their vegetable nature. 
After soaking in dilute hydrochloric acid, they can be sectioned 
and examined, the coating, sometimes- peeling off like a shell, is 
occasionally perforated like a sieve, or it may gradually dissolve 
away. Having removed the coating, we find in Halimeda, a series 
of unicellular filaments which are constricted at intervals. At 
these constrictions, the cells branch out laterally, something like a 
fan. and the final ramifications of adjacent filaments, approxi- 
mating each other, form the surface on which 
the carbonate of lime is deposited. Besides 
these constrictions in each filament, the 
whole mass is also constricted at intervals. 
making a necklace in which the joints grow 
gradually smaller. The different forms of 
these articulations mark the species. In the 
Neomeris dumetosa, 250 diam. 
Fig. 55. 
Codium tomentosum, 200 k 
diam. Wright collection were Halimeda opuntia, 
a tropical cosmopolitan, named from this resemblance to a prickly 
pear, and H. tridens (Fig. 52, magnified 300 diameters), in which 
the upper edge of each joint is three-toothed. 
The Udoteæ look like green fans with a short handle. The type 
