and Observations on the component Parts of Membrane. 337 



each joint, and was interposed between the cones of the coralline 

 substance, like the common cartilages of the articulations. 



From this construction it appears, that this Isis is capable of 

 great flexibility when in a recent state ; for the gristly part of the 

 bulbs is then most probably much softer, and more elastic, than 

 it appears to be in the dried specimens which are found in 

 collections,* 



The gristly substance which forms the bulbs, and the coralline 

 joints, are kept together, and are covered, by a thin skin or 

 membrane, which is continued over the whole, like a tube. The 

 joints are not, therefore, devoid of a coating, as seems to be 

 implied by the definition of Linn^us. 



Isis Hippuris. 



Part of a branch of this Ms was immersed in very dilute 

 nitric acid, and a considerable effervescence immediately took 

 place. When this effervescence had ceased, there appeared little 

 or no change in the original form of the Isis ; but the coralline 

 joints were now become a soft, compact, white, and opaque 

 membranaceous substance ; while the dark brown intermediate 

 parts retained also their form, and in other characters resembled 

 those of horn. 



The solution was colourless and transparent. When saturated 

 with pure ammoniac, it was not affected ; but carbonate of pot- 

 ash produced a copious precipitate of carbonate of lime. 



Another part of this Isis was exposed to a low red heat, in a 



* It must here be observed, that the articulated structure abovementioned, is not to 

 be found in those parts which form the main stem, with its larger branches; the 

 joints in those parts being consolidated, so as to constitute a strong and rigid trunk, 

 upon which the whole fabric is supported. 



Xx 2 



