20 
Tank No. 21. 
Fig. 16. Isis neapo- 
litana on a stone, 
with expanded po¬ 
lypes. 
The hark has died off at 
the lower end and the 
skeleton is therefore vi¬ 
sible. J / 2 na, t* size. 
Fig. 15. Gorgonia verrucosa 
on a stone. 1/2 nat. size- Some 
of the polypes are expanded. 
The great value of the Red Coral, Corallium 
rubrum (Fig. 17), for ornamental purposes is due to 
its beautiful colour and to the hard texture of its 
skeleton, enabling it to take a high polish. The 
ancients valued corals greatly, but they had a wholly 
erroneous idea of their na¬ 
ture , an idea shared even 
now by many people; they 
considered the Coral to be a 
plant, which remained soft 
while in the sea, but which 
became hard suddenly on 
being taken out of the 
water. But if a branch be 
examined, as soon as it 
has been freshly fished, it 
will be found to be en¬ 
veloped by a coating, also 
of red colour, just as the 
wood of a tree is enveloped 
by its bark. Such a branch 
placed carefully in a large 
vessel of fresh sea-water 
will after a short time shew 
at numerous points of its 
surface the expanded coral- 
animals each with its eight 
feathery tentacles. Each 
individual has the structure 
of a polype, as described 
above; and is organically 
connected with all the others 
by means of canals, which 
transmit food from one 
living polype to the other. 
In the covering, besides 
these canals, are numerous 
microscopic spindle-shaped 
particles of carbonate of lime; 
the axis is formed by a fusion 
of such particles. This 
structure of the coral is 
very readily distinguished 
under the microscope, by 
the aid of which instrument 
all spurious imitations can 
be easily detected. Corals 
reproduce by means of eggs 
or by buds. There exist 
Fig. 17. Corallium rubrum 
on a stone with expanded 
polypes, 1/2 nat. size. 
