3o6 TOILERS IN THE SEA. 



lid-like mandible, with plain rounded margin, has 

 no power of grasping, and could not detain for a 

 second the active worms which are sometimes cap- 

 tured by the articulated kinds. Their service for 

 the colony must lie in some other direction. Even 

 the fixed transitorial forms, in which the beak and 

 curved mandible are present, must be inefficient for 

 this work, from their want of mobility, whilst in 

 many of them the parts concerned in the act of 

 prehension are but slightly developed. The articu- 

 lated avicularia, however, are undoubtedly grasping 

 organs ; and the presence of the tactile tuft, between 

 the jaws, must be taken to indicate that capture in 

 some form or other is their function. They have 

 been seen to arrest minute worms, and hold them 

 for a considerable time with a tenacious grip, as if 

 with some ulterior object ; but what the object may 

 be it is difficult to decide. On the whole, I am 

 inclined to regard the avicularia as charged with a 

 defensive rather than an alimentary function. They 

 may either arrest, or scare away, unwelcome visitors. 

 Their vigorous movements, and the snapping of their 

 formidable jaws, may have a wholesome deterrent 

 effect on loafing annelids, and other vagrants ; 

 whilst the occasional capture of one of them may 

 help still further to protect the colony from dan- 

 gerous intrusion." The vibraculum, or moveablc 

 bristle, is related to the avicularium, and a line of 



