3IO TlMEHRl. 
tioned. The various forms of coral or coral-like 
animals are strictly marine ; but a few species, 
which inhabit the estuaries of rivers, have become 
adapted to more or less brackish water, and flourish 
therein. 
The Zoophytic range is almost unlimited, spreading 
from the icy poles to the Equator, and from the surface 
to the abysses of the ocean ; and while special forms 
are characteristic shore or surface organisms, others are 
only known from considerable depths, often reaching to 
many hundreds of fathoms. For the Zoophytes, how- 
ever, as for all other groups of marine organisms, the 
zone of greatest development lies along the superficial 
area, from the surface to a depth of about thirty to forty 
fathoms, where the conditions of life, such as presence 
of light, a moderately high temperature, and abundance 
of food, are most favourable. In one great group, that 
of the reef-building corals, the zone of life itself is still 
more sharply circumscribed, since the limit is practically 
reached within 30 north and south of the Equator, 
where the minimum temperature at a depth of: thirty 
fathoms is about 68 p F. Purity of the water and freedom 
from mud in suspension, are almost essential conditions 
for Zoophytic life ; and scarcely less important than these 
is the condition of the water as regards its salineness, 
since a discharge of large quantities of freshwater 
from large rivers, exercises a marked deterrent effect on 
the development of these organisms. In the prevalence 
of unfavourable conditions such as these, viz., large 
quantities ot mud in suspension and on the shore bed, 
and the discharge of immense quantities of fresh water 
from the rivers, must be sought the explanation of the 
