122 
ON THE ORGANS OF RADIATED ANIMALS. 
their bodies, or into separate spaces, or ramified organs, destined for this important 
function. The sexes are united in the same individual, and in the highest class 
a perfect hermaphrodism exists. Cuvier used the term Radiata to indicate the 
stellular arrangement of their external parts and internal organs, whilst the 
circular disposition of their nervous system around the entrance to their stomach, 
induced Professor Grant to propose the term Cydo-neura for this sub-kingdom, 
which he limits to the following classes . 
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The Skin soft, 
transparent, or 
gelatinous. 
The Skin 
coriaceous or 
crustaceous, 
and armed 
with spines. 
*5 
Class I. 
ZOANTHIDA. 
" Animal floriform, fixed or free, 
capable of moving by the action 
of a terminal sucker; digestive 
sac with a single opening, and 
surrounded by a circle of coloured 
- tubular tentacula. 
Class II. 
Arachnoderma. 
Animals with a simple gelati¬ 
nous structure, organised for 
floating through the ocean by 
membranous sacs or vibratile 
cilise; body secreting an irritat¬ 
ing fluid, which produces urti- 
cation by contact with the skin. 
Class III. 
Echinoderma. * 
Animals of an extremely com¬ 
plicated structure, for the most 
part free, ambulatory, and pre¬ 
daceous, provided with a highly 
organized integument, and hav¬ 
ing a skeleton of many thousand 
pieces; they are furnished with 
tubular feet for walking, or pre¬ 
hension, with a distinct vascular 
system; and some have visual 
organs. 
The Zoanthida form the passage from Zoophyta to Radiata. They have a cylin¬ 
drical fleshy body, truncated at both extremities ; the posterior or inferior serves in 
some genera as an organ of attachment to submarine bodies, whilst in others it 
is converted into a muscular disc for locomotion; the anterior or superior 
extremity of the fleshy body develops numerous tubular, simple, or ramose 
tentacula, often adorned with the most vivid colours, and disposed in one or 
