112 Mr. W. Percy Sladen on the 



rechinus granulans, with its mucus-sacculi situated midway 

 upon the stem, is a form derived and developed from the 

 simple and more compact condition of the organ, such as is 

 presented in the pedicellaria of the E. nielo type, and of which 

 the early immature phase of the Sphcerechinus granularis- 

 pedicellaria, which has the mucus-sac situated immediately 

 below the valvate head, is the representative. 



In sequence to these conclusions it is perhaps not straining 

 the argument too far to adduce it as an indication of the 

 ancestry of the latter species from some more primitive Echinus 

 type. 



On the Functions of the Pedicellaria? of Echinus in general. 

 — The observations above recorded and the conclusions de- 

 duced therefrom may lead not inaptly to a few remarks on 

 the companion forms of pedicellaria?. Mr. Alexander Agassiz 

 was, I believe, the first who by actual observation assigned 

 the true function of any of these organs. He stated that he 

 had watched the pellets of exuvise being passed along the 

 test and removed from the body of the Echinus by means of 

 pedicel larise. Unfortunately Mr. Agassiz leaves the matter 

 without saying which of the forms of this appendage was the 

 agent employed. I also have seen the same operation per- 

 formed ; and it was always the pedicellarice tridentes that came 

 into use for the purpose ; indeed the most superficial exami- 

 nation would suggest that these alone could be employed for 

 such a service, neither the p. globiferce nor the p. triphyllai 

 having valves capable of grasping so large a body as the 

 ejected pellets in question. On the other hand the jaws of 

 the p. tridentes are admirably fitted for the purpose ; and that 

 this is the chief use of that form of pedicellaria there seems 

 but little doubt. 



The use of the pedicellaria? globiferce has been indicated in 

 the preceding pages. 



Lastly we have the ped. triphyllai. Unfortunately my own 

 observations have not yet enabled me to make out their special 

 function with any degree of certainty ; but their small size, as 

 well as their general behaviour, lead me to the decided im- 

 pression that their principal use is that of seizing the smaller 

 particles of foreign matter, which of necessity have eluded 

 the more rigid as well as more specially organized forms above 

 mentioned, and of casting their captures either directly away 

 from the test or, perhaps more probably, into the mucous 

 pellicle formed by the discharge of the pedicellaria? globiferce 

 under the circumstances previously noted. That the ped. 

 triphylla? should be used, as some writers have maintained, 



