VIBRACULUM. 101 



and closing that which was formerly the door 

 of the cell, but which is now more appropriately 

 termed the mandible, since it is seen to be 

 continually opening and shutting, with a sharp 

 snap, and often with some minute creature, in 

 its grip. It seems probable, therefore, that 

 the function of this organ may be t<> .protect' 

 the colony from hostile intruders. 



Vibraculum. There is yet another 

 departure, a further modification of the Bird's- 

 head organ, to be described. It consists in 

 a further development of the mandible, and its 

 adaptation, evidently for a different purpose 

 from that of prehension. The mandible 

 becomes greatly prolonged, to such an extent 

 that it has more the appearance of a sword or 

 stick, guarding the various members of the 

 colony with which it is associated. The idea 

 is borne out by the circumstance that this 

 sword or Vibraculum, as it is called, is 

 constantly waving from side to side. If this 

 vibracular organ be now compared with its 

 point of departure, viz. : the Polypide and cell, 

 one can hardly fail to be struck by the 



