304 ZOOLOGY. 



THE BLUE BARNACLE. 

 (Pentalasmis Vitrea.) 



Notwithstanding its specific name, this species of 

 barnacle has of all others the softest covering its shell 

 being little more than cartilaginous. It is uniformly 

 of a blue-green colour ; and the cirri of the contained 

 animal are brown. It adheres to floating bodies by its 

 long pedicle, and in large clusters, (as is usual with 

 this family of shell-fish,) but it is remarkable of this 

 particular species, that it has also the power of con- 

 structing a common aeriferous float, which serves for 

 an entire cluster of shells, and enables them to re- 

 main on the surface independent of any extraneous 

 aid. 



It has been said, that this buoy, or float, is an " ex- 

 traneous substance, and probably of vegetable origin ;" 

 but facts which have come under my notice prove that 

 opinion to be incorrect. The exterior of the structure 

 is smooth, colourless, and elastic, and of about the 

 consistence of dense jelly ; * its interior is cellular, each 

 cell containing a quantity of air. When employed in- 

 dependently it has a globular form ; but its shape is 

 often influenced by the body to which it is attached, or 

 which may serve as its nucleus : thus, we met with 

 some of these barnacles attached by their aeriferous 

 float to the skeletons, or fulcra, of Velella Mutica, and 

 it was evident, that as the barnacles grew heavier, or 

 the fulcra of Velella decayed, the aeriferous float in- 

 creased in size ; until the velella, instead of being the 

 supporting body, became a mere shred, lodged within 

 the buoyant appendage of the barnacles. 



* I believe it will be found, that the membrane covering the pedicles 

 of the clustered barnacles is extended over the surface of the aeiiferous 

 float. 



