ANIMALS. 21 
of the polyps. The first sub-class may be conveniently divided into two orders, 
Hydroida and Actinoida ; but the second does not as yet appear to be resolvable into 
more than one, for which it is intended.to use in a popular sense the name Aryozoa, 
originally proposed for the group itself by Ehrenberg. In the first and lowest order, 
Hydroida, digestion is performed by the secretion of a simple sac excavated in the 
gelatinous and granular substance of the animal’s body. In the second, Actinoida, the 
digestive sac, which, like the first, throws out the rejectamenta by the same aperture 
as that which receives the nutriment, is suspended by a series of vertical folds of 
membrane, in a distinct abdominal cavity, to the outer parietes of the body. In the 
sub-class Ciliobrachiata, the alimentary canal, which is likewise suspended loosely in 
an abdominal cavity, is provided with a distinct mouth and outlet.’ 
It is uncertain whether the whole of the orders just noticed have representatives 
amongst the Corals hereafter to be described. There are strong objections to any of 
them being considered as Hydroidas; but there is nothing to oppose the placing of 
most of them in the other divisions. 
Sub-class NUDIBRACHIATA, Farre. 
Waiving the /ydroida, for the reason just stated, it is proposed to pass at once to 
the order Actinoida established by Dana, who divides it into two sub-orders, Actinaria 
and Alcyonaria. 
Sub-order ACTINARIA, Dana, 1847. 
ZOOCORALLIA POLYACTINEA, Lhrenberg. 
Zoantua, Blainville. 
Les ZoantTArReEs, Audouin et Milne Edwards. 
ZoopuHyta HELIANTHOIDA, Johnston. 
Diagnosis.—“< Tentacles six, twelve, or more m number, not papillose (with few 
exceptions), and perforate at the apex; often coralligenous ; coralla calcareous, very 
rarely corneous, cells radiate with lamelle.’”” (Dana.) 
The members of this division are represented on the British coasts by the naked 
Actinias or Sea Anemones, everywhere distributed on our rocks; by the single species 
Zoanthus Couch, which seems to be confined “to the Cornish part of the British 
Channel ;” and by a few forms of lamelliferous Corals rarely to be met with in northern 
' Vide Owen’s Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, 
p. 82. 
* Structure and Classification of Zoophytes, p. 113, 1847. 
