CCELENTERA TES. 
5i8 
animal life, in passing at death into their elementary constituents, leave no visible 
traces of their existence, the corals, or at least the numerous reef-making forms, 
build monuments which last for hundreds of thousands of years, and may be 
said to attain their greatest importance in the influence they exercise upon the 
life and development of the human race. Professor Haeckel has described the 
magical effect of a first sight of a shallow coral-reef, enjoyed by him on the coasts 
of the Red Sea, where a long bank of coral runs parallel to the shore. The 
waves break upon these barrier-reefs, the uneven edges of which lie just below 
the surface of the water, and their position is thus clearly marked by the line of 
surf produced. The outer side of the reef, which is exposed to the full force of 
the waves, descends steeply, but the inner side, washed by comparatively quiet 
water, slopes gently down; the canal formed between the reef and the coast being 
as a rule so shallow and calm that the full splendour of the garden of corals at 
its bottom can be seen through the limpid water. 
All reef-forming: corals inhabit waters which in winter do not sink below 
a temperature of 68° F., the maximum summer heat in the Pacific Ocean 
being 86°. Two lines to the north and the south of the Equator, which would 
connect points where the winter - temperature does not sink below 68°, waving 
in and out according to the currents, would enclose the zone of the reef-forming 
corals. Most of the stock - forming corals described above live exclusively 
within these limits of temperature, a fact that explains their rare occurrence in 
the Mediterranean, which is so favourable to other forms of animal life. The 
richest coral regions lie in the middle hottest zone, that is between 15° and 18° 
north and south of the Equator, where the temperature does not fall below 
72° F. The Fiji Islands fall within this region, and possess reefs extraordinarily 
rich in corals. The star-corals and brain-corals there reach their greatest develop¬ 
ment, while the madrepores are found as bushes, cups, or leaves, the latter often 
attaining a breadth of over six feet. In the Sandwich Islands, which lie outside 
of the hottest zone, the corals are less luxuriant and varied. The genera of corals 
found in the Indian Ocean and the Red Sea, as well as on the coast of Zanzibar, 
are essentially the same as those in the Pacific. The corals of the Gulf of Panama, 
although not in the hottest zone, have the character of the Pacific corals, and are 
different from those of the West Indies. 
When the two Fosters and Cook discovered the coral islands of the South 
Sea, they were of opinion that the minute creatures to which these owe their 
origin began to build at unfathomable depths, gradually bringing their structures 
up to the surface of the water. They thus thought that the same species were 
able to live at different depths. Recent researches have disproved this; and we 
now know that although many different animals live at enormous depths, all 
such are specially adapted to the conditions of life at those depths. Animals 
adapted to life at a great depth cannot exist at the surface. The number of 
deep-sea polyps is small, and among them there are no species forming reefs; 
and authorities are now agreed that reef-building corals can only live at moderate 
depths and within certain latitudes. One of the principal requirements is pure 
sea-water, some species flourishing in the canals between the reefs and in the 
shallower water of the lagoons, whereas others require the open sea. Corals 
