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CLASS IH.— ORDER III. 
smaller than the second or horny articulations ; these 
last are always opaque, of a deep brown colour, and 
easily distinguished from the preceding by the great 
difference which exists in their composition. They 
appear destined to give to the Isideas, or genera 
of the present order, the power of yielding to the 
movements of the waters, and thus, by a slight flexibi- 
lity, to make up for their want of solidity : this flexi- 
bility ceases when the Polypidoms are dry, then in- 
deed their fragility is such that it is impossible to bend 
them so as to preserve them in a herbal. In general, 
the Isideas are more fragile in proportion to the dif- 
ference that exists between the two substances that 
compose the axe. 
The rind, or external envelope, is of a soft and fleshy 
consistency in the living Polypidom ; by desiccation 
it becomes cretaceous and friable, not adhering to the 
axe, from which it separates with so much facility, 
that some authors have imagined it was never entire. 
It is very rarely so found in the collections, but in 
its natural state the case is different ; then the stem 
and the branches of this articulated Polypidom are 
covered through their whole extent with a fleshy en- 
velope, animated with swarms of small and brilliant 
polypi. This envelope or rind is always very thick, 
both when taken from the sea, and after desiccation. 
It may not be useless to remark in the Isidean or- 
der a circumstance equally observable in that of the 
Gorgonias, which is, that where the rind is thin it 
always adheres to the axe, and separates from it with 
proportionate facility as the rind increases in d thick- 
ness. Thus the Isideas and the Plexauras, the Gorgo- 
nias and the Meliteas, exhibit a striking analogy in the 
