Ixxviii INTRODUCTION. 



developed. The articulated avicularia, however, are un- 

 doubtedly grasping organs*; and the presence of the tac- 

 tile 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 \\ itli 

 some ulterior object ; but what the object may be it is 

 difficult to decide. Dr. Johnston suggested that they 

 may assist in providing supplies of food, seizing "circum- 

 fluent animalcules," and retaining them until, ' ' enfeebled 

 or killed by the grasp/' the ciliary currents may bear them 

 to the mouth. But the avicularium is not fitted to cap- 

 ture the extremely minute organisms on which the poly- 

 pides feed ; and even could they be captured and rendered 

 helpless, there would be many chances, placed as the ap- 

 pendages usually are, against their coming within the 

 attraction of the ciliary vortex. The worms, which seem 

 to be the commonest victims, could only be utilized as 

 food by being retained until, decomposition having set in, 

 the particles of decayed matter might diffuse themselves 

 through the surrounding water, and find their way, in 

 greater or less degree, to the stomachs of the polypides. 

 But the supplies of nutriment in the water of the ocean 

 must be ample and unfailing, and no better provision for 

 appropriating them than the ciliary whirlpool can well be 

 imagined. Unless we can suppose that a peculiar diet is 

 necessary for the species furnished with the prehensile 

 appendage, it is hardly probable that the ordinary ar- 

 rangements would have to be supplemented by the service 

 of such uncertain purveyors. And should they be feeders 



* " When touched with a needle the beak generally seized the point BO 

 firmly that the who'e branch might be shaken." DARWIN. 



