58 CELLULARIID^E. 



of the cell they stretch diagonally downwards, reaching to 

 the median line, where the two opposite rows meet. The 

 vibracular cell is of an elongate-oval figure above; and this 

 portion of it bears some resemblance to a delicate bivalve 

 shell resting on its dorsal surface, and slightly gaping. 

 Below it is much produced and attenuated. At its upper 

 extremity there is a cleft in which the movable seta works; 

 and when at rest it lies in the groove, which passes from 

 the terminal notch downwards. 



The size of the vibracula in the genus Caberea is not 

 their only peculiarity. In C. Boryi (and probably in 

 the other species) they differ from the same appendages 

 in the kindred genera physiologically as well as in 

 form and size. Whilst the vibracula of Scrupocellaria 

 act independently of one another, those of C. Boryi 

 move together with perfect regularity; they act not 

 individually, but in companies, obedient to a common 

 impulse. After a short interval of quietude all the 

 vibracula on a shoot are seen to start into sudden activity, 

 swinging themselves round simultaneously to the front of 

 the cells, and then sweeping backwards again and resuming 

 their former position. After another interval the same 

 synchronous and perfectly regular movement takes place, 

 and so on continually. There is something positively 

 startling, after the absolute quiet, in the sudden simulta- 

 neous rush of the whole host of vibracula into energetic 

 action *. 



In this species, then, not only are the individual appen- 

 dages highly developed, but the whole company of them 

 attached to a colony are brought into combined and harmo- 

 nized action. It must be left to future observation to 

 determine the precise structural conditions on which these 



* See a paper by the author, " On the Movements of the I'ibraciila in 

 Cuberca Boryi" Sue., in the Quart. Journ. Mice. Sci. for Jim. 1878. 



