234 CLASS 111.— 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^ thick- 

 ness. Thus the Isideas and the Plexauras, the Gorgo- 

 nias and the Meliteas, exhibit a striking analogy in the 



