142 Transactions of the Royal Society of Victoria. 



will be made as to the direction of movement. Further, 

 in describing movements of rotation it will be found very 

 convenient to use the terms right-handed and left-handed, 

 as is done in connection with the rotation of the plane of 

 polarization. So when rotation occurs in the direction of the 

 hands of a watch, as seen by the observer, it will be called 

 right-handed, and when in the opposite direction, left- 

 handed ; and the Labial Palp, for instance, according to its 

 rotation, will be spoken of as right-handed or left-handed. 



I. — Labial Palps. 

 1. — Inner Palps. 



If a Palp is detached as near its base as possible, and laid 

 on a plate with the liquid from the shell, then its motions 

 are easily observed. 



The movement is one of regular rotation, the palp 

 revolving about one end in a steady manner, and in a 

 definite direction. There may be forward, or backward, or 

 lateral movement combined with this, but when once the 

 palp has fairly become accustomed to its free condition of 

 existence, rotation is its characteristic movement. This 

 rotatory motion is probably due to the fact that the basal 

 (cut) end is destitute of cilia, and so there is a tendency to 

 turn round that spot as on a pivot. The palp, however, can 

 also rotate upon its tip, and we can hardly account for 

 making it the pivot on purely mechanical grounds. 



The right and left inner palps detached turn imvards, the 

 left turning to the left, while the right turns to the right. 

 If there are obstacles in the way, such as dirt-particles in the 

 water, or solid bodies of any kind, then the sensitive tip, 

 ever, seemingly, on the alert, soon backs out and clears away 

 from it, even although it should involve a change of course. 

 Thus, I have seen a palp, when placed in a dirty liquid, turn 

 backwards for a short distance, until it had shaken itself 

 clear of adhering rubbish, and then go forward in its regular 

 course, as if nothing had happened. If either palp is reversed, 

 then it might be anticipated that the direction of movement 

 would be also reversed, but as the result of several trials it 

 was found that the direction was the same, the left inner 

 being right-handed and the right inner left-handed. 



Numerous continuous observations were made, over 

 extended periods of time. It generally happened that the 



