(i Mr. G. J. Romanes and Prof. J. C. Ewart. [Mar. 24, 



tliis action twist their semi- spirals in the same direction, and by their 

 concerted action serve to drag the disk and the remaining rajs over 

 themselves as a fulcrum. Other species of star-fish, which have not 

 their ambulacral suckers sufficiently developed to act in this way, 

 execute their righting movements by doubling under two or three of 

 their adjacent rays, and turning a somersault over them, as in the 

 previous case. Echinus rights itself when placed on its aboral pole, 

 by the successive action of two or three adjacent rows of suckers, so 

 gradually rising from aboral pole to equator, and then as gradually 

 falling from equator to oral pole. S'jpatangus executes a similar 

 manoeuvre entirely by the successive pushing and propping action of 

 its longer spines. 



2. Stimulation, — All the echinoderms that we have observed seek to 

 escape from injury in a direct line from the source of stimulation. If 

 two points of the surface are stimulated, the direction of escape is the 

 diagonal between them. When several points all round the animal are 

 simultaneously stimulated, the direction of advance becomes uncertain, 

 with a marked tendency to rotation upon the vertical axis. If a short 

 interval of time be allowed to elapse between the application of two 

 successive stimuli, the direction of advance will be in a straight line 

 from the stimulus applied latest. If a circular band of injury be 

 quickly made all the way round the equator of Echinus, the animal 

 crawls away from the broadest part of the band — i.e., from the greatest 

 amount of injury. 



The external nerve plexus supplies innervation to three sets of organs 

 — the pedicels, the spines, and the pedicellariee ; for when any part of 

 'the external surface of Echinus is touched, all the pedicels, spines, and 

 pedicellariee within reach of the point that is touched immediately 

 approximate and close in upon the point, so holding fast to whatever 

 body may be used as the instrument of stimulation. In executing this 

 combined movement the pedicellariee are the most active, the spines 

 somewhat slower, and the pedicels very much slower. If the shape of 

 the stimulating body admits of it, the forceps of the pedicellariee seize 

 the body and hold it till the spines and pedicels come up to assist. 



And here we have proof of the function of the pedicellariee. In 

 climbing perpendicular or inclined surfaces of rock covered with 

 waving sea- weeds, it must be no small advantage to an echinus to be 

 provided on all sides with a multitude of forceps adapted, as described, 

 to the instantaneous grasping and arresting of a passing frond ; for, in 

 this way, not only is an immediate hold obtained, but a moving piece of 

 seaweed is held steady till the pedicels have time to establish a further 

 and more permanent hold upon it with their sucking disks. That this 

 is the chief function of the pedicellariee is indicated by the facts that, 

 1st, if a piece of seaweed is drawn over the surface of an Echinus, 

 this function may clearly be seen to be performed ; 2nd, the wonder- 



