294 



ORDER PEDUNCULATA ; BARNACLE, ETC. 



easily understood, when it is borne in mind how greatly the 

 friction will be increased, when the water, instead of being 

 ploughed by a smooth surface, is held (so to speak) by excre- 

 scences, such as those represented in Fig. 516. The commonest 

 species, Pentalasmis anatifera, is the one respecting which so 

 many absurd stories were formerly told (Vol. I. p. 16). The 

 peduncle sometimes grows to the length of two or three feet ; and 

 it possesses a considerable degree of contractility, enabling the 

 animal, by its means, to change its place, in some degree, by the 

 shortening, extension, or bending, of the footstalk. A large log 

 of timber covered with these animals, twisting and diverging in 

 all directions, and so close as to hide the surface of the log, is a 

 curious sight, looking like an enormous collection of Serpents. 



FJG. 517- CINERAS CRANCHII. 



Fio. 51(5. Group of BARNACUCS, attached to a ship's 

 bottom. 



In the Cineras, the mantle has somewhat of a cartilaginous tex- 



