364 THE LIVING ANIMALS OF THE WORLD 
in a condition of healthy growth, yielding a spectacular effect that vies with that of any 
floral parterre. Sometimes large areas, acres upon acres in extent, may be covered with one 
almost uniform purple, green, brown, or other coloured growth of the branching stag’s-horn 
species. The aspect presented is not unlike that of a heath-covered common. 
In addition to the solid, calcareous-skeletoned Madrepores, or “ Stony Corals,” as they are 
often termed, there are a number of species in which a skeleton composed only of loosely 
aggregated calcareous spicules 
is produced. The so-called 
Flexible Corals, or Sea- 
fans, belong to this category, 
as also the precious Coral 
OF Commerce. In the last- 
named species the solid, 
brilliantly coloured skeleton 
so much prized as an article 
of jewellery is deposited as a 
supplementary basis outside 
the tissues by which the star- 
patterned skeletons of the 
stony corals are secreted. 
A group which demands 
brief notice is that of the 
Hydroid Polyps. These 
include the majority of the 
Jelly-fishes, a few coral- 
secreting species, and the or- 
ganisms whose seaweed-like 
horny skeletons, known as Sea- 
FIRS, are, in common with those 
of Sea-mats, included among 
the flotsam and jetsam on 
ovory soa-beach. In the 
Common Hydra, or Fresh- 
tYATER Polyp, an exceptional 
fresh-water representative of 
this group is presented. It may be likened to a tiny sea-anemone, having, when extended, 
a slender foot-stalk and long thread-like tentacles. Like a sea-anemone, it will shrink up 
when disturbed into a mere button of jelly. Its organisation is more simple than that of 
the anemone, its body-cavity being a simple sac, without any intucking of the orifice, or 
strengthening by supplementary membranous partitions. A similar simple structural plan 
is characteristic of all the organisms belonging to the series. An interesting phenomenon 
connected with the fresh-water hydra is the circumstance, demonstrated now over a century 
ago, that, if one of these animals be cut up into little pieces, each separate fragment is 
capable of repairing itself and growing into a new polyp. 
The Jelly-fishes, or Medusas, and their allies would appear at first sight to possess but 
little structurally in common with the Coral-polyps and Sea-anemones. In their most familiar 
form they are represented by a more or less translucent bell-shaped body, which drifts with 
the current or propels itself through the water by its alternate expansions and contractions. In 
the centre of the lower surface, occupying the position of the bell’s clapper, a poh’p-like, 
tubular mouth is usually discernible, and this is frequently surrounded by a circle of tentacles, 
sometimes simple and sometimes elaborately ramified. Long, thread-like tentacles are also 
commonly develojaed around the margin of the swimming-bell. 
Phito by W, Saville-Keniy F.Z.S.'] 
A QUEENSLAND STAR-CORAL 
This species in life is of a pale lemon-yelloiv tint 
