102 CORALS AND CORAL ISLANDS. 
The Hydroids were long considered polyps. But they 
have been found to give origin, with few exceptions, to Weduse, 
or jelly-fishes, and it is now proved that they are only an 
intermediate stage in the development of Medusz, between 
the embryo state and that of the adult or Medusa state. The 
Millepores afford, therefore, examples of coral-making by spe- 
cies of the class of Acalephs. Many of these Meduse and 
their Hydroids will be found illustrated in the admirable work 
of Alexander and Mrs. L. Agassiz entitled “ Sea-Side Studies,” 
—an excellent companion for all who take pleasure in sea- 
shore rambles. 
The Hydra is the type of a large group of species. It buds, 
but the buds drop off soon, and hence its compound groups 
are always small, and usually it is single. But other kinds 
multiply by buds that are persistent, and almost indefinitely 
so; and they thus make membranous coralla of considerable 
size and often of much beauty. 
The species here figured, Hydrallmania falcata (formerly 
called Plumularia falcata), is one of them. Along the 
branches there are minute cells, each of which was the seat of 
one of the little Hydra-like animals (in this not a fourth of a 
line long) having usually short tentacles spread out star-like. 
Other kinds are simple branching threads, and sometimes the 
cells are goblet-shaped and terminal. The Tubulariz grow 
in tufts of thread-like tubes, and have a star-shaped flower 
at top often half an inch in diameter, with a proboscis-like 
mouth at the centre. In Coryne, a closely-related genus, the 
tentacles are shorter, and somewhat scattered about the club- 
shaped or probosciform head of the stem, so that the animal 
at top is far from star-shaped or graceful in form. 
To the animal of the Coryne, that of the very common, and 
often large, corals, called Millepores, is closely related, as first 

