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NOTES ON THE OPHIUKANS, OR THE SAND 
AND BRITTLE STARS. 
By Professor P. MARTIN DUNCAN, M.B. (Lond.) F.B.S., &c. 
PLATE YII. 
T HE marine invertebrata, which are called Echinodermata, on 
account of their possessing a more or less perfect covering 
of sometimes spiny, and usually geometrically shaped pieces of 
carbonate of lime, form a very large and natural group, which 
is very well defined on one and not so perfectly on the other 
side of the zoological scale. 
Cuvier made the Echinodermata to form a class of the sub- 
kingdom Radiata, and Agassiz insisted on retaining this nomen- 
clature, which is still employed by some excellent naturalists. 
The star-like markings and form, the arrangement of the 
structures in a raylike manner around the mouth, and the 
presumed absence of any two-sidedness, apparently so character- 
istic of the sea-anemones, corals, jelly-fish, and Echinoderms, 
rendered the Radiate sub-kingdom very readily separable from 
the worms on the one hand, and from the shapeless lower animals 
on the other. Like other abstract matters, classificatory zoology 
has its phases, grooves, fancies and fashions, although its solid 
progress depends on a correct balance of embryological and 
morphological learning under the influence of a method of 
judicious comparison. 
There is no doubt that the Radiata were made to include 
some groups of creatures whose classificatory union was in- 
congruous, and that those possessing a radiate form were 
associated with the shapeless, and this necessitated the limita- 
tion of the sub-kingdom. Then Leuckart, acting under a lively 
philosophical impulse, insisted, from the study of the structures 
of some of the most important Radiata, that they were positively 
not “ all round creatures,” but were two-sided or bilateral. The 
Echinodermata were shown not to be truly Radiate animals, and 
he made a special group of them. The Actinozoa and Hydrozoa 
were separated from the Echinodermata by their gastric 
peculiarities, and their cavity with a sole entrance — their hollow 
bowel — gave them the name of Coelenterates. Broken apart, 
the Radiate sub-kingdom became a republic, and the group 
NEW SERIES, VOL. II. — NO. VIII. Z 
