POLYPIFERA. 953 
to foster this error. But the processes are in no respect 
similar: the insect, under the guidance of an unerring in- 
stinct, resulting from its peculiar organization, constructs its 
cells ; but the polype is incapable of forming, or even modify- 
_ ing, its support or cell in the slightest degree. The polypidom 
is secreted by the animal tissues, in the same manner as are 
the bones in the vertebrated animals, without the individual 
being conscious of the process. If a piece of white coral be 
immersed in dilute hydrochloric acid, the calcareous part is 
dissolved, and the secreting membrane, in the form of a flocu- 
‘lent substance, is seen attached to the undissolved part; even 
in some coralline marbles of incalculable antiquity, the animal 
membrane may, in this manner, be detected.* 
From the delicate and perishable nature of many of the 
gelatinous zoophytes, numerous tribes may have inhabited 
the seas, which deposited the fossiliferous strata, and yet no 
indications of their existence remain ; while, of others, but 
obscure traces of their structure are likely to be detected. 
The Polypifera are separated into two natural groups or 
classes ; viz. the ANTHOZOA (flower-animals), and the Brrozoa 
(moss-animals), or Potyzoa. 
The Anthozoa are polypes of the most simple type of 
structure. The body consists of a symmetrical gelatinous 
Sac, capable of contraction and expansion, with one aperture 
or mouth, which is encircled by tentacula. The Hydra, or 
fresh-water polype (Word. p. 600), is a familiar example of 
a single, locomotive, anthozoan animal. In the compound 
or aggregated forms, the body is either inclosed in a horny 
Sheath (ex. Sertularia, Wond. p. 615), or is supported by 
a lamellated calcareous endo-skeleton (ex. Fungia, Wond. 
Pp. 623, pl. vi. fig. 15), or the soft parts invest a stony axis 
(ex. Madrepora, Wond. p. 620), or a horny flexible frame- 
work (ex. Gorgonia, Wond. p. 616). 
The Anthozoa are subdivided into three orders, which are 
* See Pict. Atlas, pl. xxxiv. fig. 2. 
