ON THE SKELETONS OF ZOOPHYTES. 
181 
contrivance to support their fragile structure against the violence of the waves; 
hence the law impressed on their organism to form lateral supports at certain 
intervals, which gives rise to the horizontal laminae that form so singular 
a feature in the skeletons of this family. When the tube has been developed 
to a certain height, the Polyp commences the construction of its strengthen¬ 
ing plates. This singular piece of masonry is accomplished by the animal 
expanding the Calcifying membrane to a certain distance outwards, then 
folding the membrane upon itself, so as to bring the inner surfaces in contact, it 
returns to its original position, and resumes its tubular form; the membranous 
septa are soon impregnated with Calcareous particles, and intimately soldered 
together, to afford the necessary support to the growing edifice. 
The regularity observed in the construction of these laminae shews that they are 
formed by a simultaneous effort of the Polypi on the same plane. A mechanical 
advantage is thus gained; for as the margins of the membranes expand outwards, 
they meet each other, and, thus united, form an uninterrupted floor extend¬ 
ing across the entire extent of the Polypary, which serves the purpose of cross 
beams to bind the columnar structure together in all its parts, thus affording 
additional security to another story of tubes to be raised upon this newly-formed 
stage. The Polyp does not occupy the entire tube, but only the last-formed 
chamber, the ancient portion of the cylinder being partitioned off at various 
distances by Calcareous septa, like the polythalamous shell of a Nautilus or 
Ammonite. The true Lithophytes have a massive skeleton composed chiefly of 
the Carbonate of Lime, with a small portion of the Phosphate, deposited in an 
albuminous material, and moulded into a variety of forms. The surface of this 
Calcareous mass develops one or more Polypiferous cells, divided by lamellae, 
which emanate from a common centre, and radiate to the circumference. The 
magnitude and position of the Polyps is therefore indicated by the provision thus 
made in their skeleton for lodging and protecting these delicate and highly 
sensitive organs. The form and position of these cavities being permanent in the 
different genera, they afford the zoologist the best characters for describing and dis¬ 
tinguishing the same. Thus they are small and extremely numerous in the Porita , 
more fully developed but less numerous in Madrepora , larger and isolated in 
Caryophyllea , where each branch terminates in a deep cell with elevated margins ; 
the globular surface of Astrea is studded over with stellate depressions, bounded 
by defined margins ; whilst in Meandrina the cells are united by tortuous channels 
that meander over the surface of these massive Lithophytes; and their vrai- 
semblance to the convolutions of the cerebrum of Mammalia has obtained for this 
genus their common name, Brainstone. In Fungia the entire surface of the large 
depressed orbicular Polypary is composed of a series of radiating vertical lamina), 
2 b 2 
