CORAL ZOOPHYTES. 85 
branches and branchlets and sprigs of flowers. There are also solid 
coral domes among the vases and shrubbery, occasionally ten, or even 
twenty feet in diameter, whose regularly arched surface is gorgeously 
decked with polyp-stars of purple and emerald green.* 
All the many shapes proceed in each instance from a single germ, 
which grows and buds under a few simple laws of development, and 
thus gives origin either to the branch, the broad leaf, the column, or 
the hemisphere. 
e. Life and death in concurrent progress.—But the more massy 
forms would not exist, and others would be of diminutive size, were 
it not for a peculiar mode of growth which characterizes most coral 
zoophy tes. 
Life and death are here in concurrent or parallel progress, a con- 
dition favoured by the existence of coral secretions. In some instances 
a simple polyp, while growing at top and constantly lengthening itself 
upward, is dying at its lower extremity, leaving the base of the coral 
bare, and destitute of any living tissues. The polyp thus continues 
rising in height, and death progresses below at the same rate, till at 
last the live polyp may be at the extremity of a coral stem many times 
its own length. ‘This process is illustrated by figures on pages 62 
and 78 of the Report on Zoophytes. 
In species which bud and form large groups, the same operation 
takes place. In some instances the summit polyp or polyps bud and 
grow, while at a certain distance below the summit the work of death 
is going on, and polyps are gradually disappearing. ‘There is thus a 
certain interval of life, the length of which interval is different for 
different species. ‘There are zoophytes which grow to a height of 
several feet, and still only the upper one or two inches are living. 
The recent polyps at the top of the column are active with life and 
vigorous in reproduction, while the more aged below, having reached 
the fixed limits of their existence, are disappearing. The enduring 
coral remains, and constitutes the basement or stage of action for 
future generations of polyps. 
But this death is not in progress alone at the base of the column or 
branch. Generally the whole interior of a corallum is dead, a result 
of the same process, as just explained. Thus, a Madrepora, although 
the branch may be an inch in diameter, is alive only to a depth of 
* See Report on Zoophytes, pp. 29 and 59-61, 
22 
