176 
ON THE SKELETONS OF ZOOPHYTES. 
is successively deposited to meet the wants of these simple beings, and is as 
necessary to the perfection of their organism, as is the internal osseous framework 
of the higher animals. 
In the study of these Protozoa , the physiologist discovers the first steps 
of that process by which Nature commences the construction and consolidation 
of a frame-work for supporting the soft tissues, by depositing earthy materials 
throughout an albuminous network ; and he discerns a striking analogy between 
the permanent condition of this process in these simple vegetable-like forms, and 
the early stages of ossification in the embryos of Vertebrata. A knowledge of the 
minute anatomy of the Spongiaria is of importance to the geologist, as it enables 
him to account for the frequent occurrence of the fossilised remains of extinct 
species in Flint-nodules, seeing that the Silex contained in their skeleton would 
act as a centre of attraction, around which Silicious particles would be deposited 
from solution through the agency of chemical affinity. 
The elegant plant-like zoophytes that convert the bed of the ocean into a 
garden of living forms, adorned with the richest and most varied hues, but for 
the most part rooted by a Calcareous base to some sub-marine body, constitute 
the class Polypifera. Their organs of support assume an infinite variety of 
forms; in some the gelatinous substance of the animal is inclosed in ramified, 
horny, tubular sheaths ; in others it develops a lace-work of minute cells spread 
in retiform expansion over the surface of marine bodies ; other zoophytes have a 
Calcareous axis inclosed in the centre of their fleshy crust; and this branched or 
globular skeleton develops in general a series of cells for lodging and protecting 
the Polypi. 
The most simple condition of the skeleton in this class is observed in Alcyonidoe; 
and the genera which compose this family, Alcyonium , Lobularia , Cydonium , 
&c., appear to form a passage from Spongiaria to the class now under considera¬ 
tion. Their frame-work consists of soft flexible filaments, interwoven to form 
the boundaries of cells, in which are lodged the numerous Polypi. In the true 
Keratophytes* as Sertidaria , Campanularia , Antennidaria , and Plumularia , 
the skeleton is in the form of an external, horny, tubular subarticulated plant-like 
sheath, for enclosing the gelatinous substance, and lodging in delicate cells, 
arranged with wonderful regularity, on the parent stem, the numerous Polypi 
that are developed from the organized axis, the Sea-pine Coralline ( Sertularia 
pineaster ), and the Bell-shaped Coralline ( Campanidaria dichotoma ), afford 
familiar and instructive examples of the external characters and internal organisa¬ 
tion of the order Vaginata. In Campanularia the plant-like stem is attached 
by a spreading root to the surface of shells or other marine bodies; the fleshy 
Polypifera with a horny axis: X^ xs > horn ; furov, a stem. 
