PHYSIOLOGY or ECHITJfODERMATA. 133 



torial or its aboral pedicels upon a glass plate placed so as to form 

 the cover of a tank which is filled with water, the Echinus will 

 remain suspended in the water holding on to the glass plate, or 

 ceiling, with as many pedicels as can be brought to bear upon 

 that surface. From the globular shape of the animal, however, 

 only a comparatively small number of pedicels can be thus 

 brought to bear ; and an insecurity of anchorage being the result, 

 the Echinus seeks to increase its hold by feeling around for 

 additional supports with its unemployed pedicels. While doing 

 so the pedicellariae may also be seen to be engaged in a similar 

 quest, and especially those near the surface of attachment ; in that 

 vicinity the little forceps are actively swaying about and snapping, 

 as if the animal knew that there was the best chance of encoun- 

 tering pieces of seaweed near the solid surface from which it is 

 depending. 



In the Eoyal Society paper it was stated that when an Echinus 

 is inverted on a flat surface under water, so that it rests upon 

 its aboral pole, it will quickly right itself by using two or more 

 adjacent rows of pedicels. The process is thus described : — " As 

 many feet upon the adjacent rows as can reach the floor of the 

 tank are protruded downwards, and fastened firmly upon the 

 floor ; their combined action serves to tilt the globe slightly over 

 in this direction — the anchoring feet on the other, or opposite, 

 rows meanwhile releasing their hold of the tank-floor to admit 

 of this tilting. The effect of the tilting is to allow the next feet 

 in the active ambulacral rows to touch the floor of the tank, and 

 when they establish their hold they assist in increasing the tilt ; 

 then the next feet in the series lay hold, and so on, till the globe 

 slowly but steadily rises upon its equator," after which it de- 

 scends as slowly into its normal position of resting upon its oral 

 surface. Now these facts led to a discussion of the questions, 

 vphether the execution of such a manoeuvre was to be con- 

 sidered due to the coordinating influence of a nerve-centre 

 having a dim sense of gravity, and feeling, as it were, this sense 

 disturbed by the unusual position in which the animal is placed ; 

 or whether the manoeuvre was to be considered due merely to 

 the serial action of the pedicels themselves, such that when the 

 globe is slightly tilted by the combined action, say, of three 

 successive pedicels. A, B, and C, ojDportunity is aff'orded for the 

 next in the sei-ies, D, E, and F, to reach the floor of the tank, 

 and, fastening upon it, to increase the tilt, so in turn affording 

 an opportunity for the next in the series, G, H, I, to establish 



