STAR-FISH AND SEA-URCHINS. 287 



which we are considering ; for not only is the force 

 exerted by the forceps during their contraction of 

 an astonishing amount for the size of the organ 

 (the serrated mandibles of the trident pedicelJaiia? 

 holding on with a tenacity that can only have 

 reference to some objects liable to be dragged away 

 from their grasp), but it is very suggestive that this 

 wonderfully tenacious hold is spontaneously relaxed 

 after a minute or two. This is to say, the pedi- 

 cellaripe tightly fix the object which they have 

 caught for a time sufficient to enable the ambulacral 

 suckers to establish their connections with it, and 

 then they spontaneously leave go ; their grasp is not 

 only so exceedingly powerful while it lasts, but it is 

 as a rule timed to suit the requirements of the 

 pedicels.* 



Concerning the physiology of the pedicellariie 

 little further remains to be said. It may be stated, 

 however, that the mandibles, which are constantly 



* A further proof that this is at least one of the functions of 

 the pedicellariae is furnished by a simple experiment. If an 

 Echinus is allowed to attach its feet to a glass plate held just 

 above its ab-oral pole, and this plate be then raised in the water 

 so that the Echinus is freelj suspended in the water by means of 

 its feet alone, the animal feels, as it were, that its anchorage 

 is insecure, and actively moves about its unattached feet 

 to seek for other solid surfaces. Under such circumstance? 

 it may be observed that the pedicellariae also become active, and 

 especially so near the surface of attachment, as if seeking for 

 pieces of sea-weed. If a piece is presented to them, they lay 

 hold upon it with vigour. 



Of course the pedicellariae may also have other functions to 

 perform, and ia a Star-fish Mr. Sladen has seen them engaged in 

 cleaning the surface of the animal ,• but we cannot doubt that at 

 least in Echinus their main function is that which we have stated. 



