1888 - 89 .] Mr D. M‘Alpine on Bivalve Molluscs. 733 
a pale brown, and there are no external indications of disruption 
or decay. 
Three specimens were taken from the mud oyster, but the move- 
ment was quite insignificant, though it was always left-handed, 
•commencing slowly, and gradually attaining the speed of one round 
in 2f minutes, after which the movement was gradually lost, the same 
irregularities as in the left inner palp, though less marked, being 
still observed. A specimen from a mud oyster exhibited no 
rotatory motion, but it progressed about \ an inch, and altered 
its shape most materially. A left inner palp rotated right-handed 
at once, and after moving upwards for a little, the tip became 
stationary, and it rotated regularly, the tip being elevated and bent 
back upon the body of the palp, pointing in an opposite direction 
to that of the movement. The slowest of fifty rounds was done in 
A\ minutes, and the quickest in 2 J minutes, the general average giving 
one round in 3J minutes. At the end of fifty rounds the palp was 
only § inch lower down, and \ inch to the left of the original posi- 
tion. This rotation continued for 24 hours. In the mud oyster the 
movement was very indefinite. 
In the left outer path the rotation was right-handed and 
very irregular, but it continued for over 53 hours. Another 
specimen, tried with the outer surface uppermost, at first moved 
laterally to the right and with slight rotation to the left ; the speed 
steadily increasing, the slowest round taking 62 minutes, the last 
and quickest (when movement was accidentally stopped) 7 \ minutes. 
Being again started it began to move bodily to the right, and after 
a little irregular movement this was continued, attaining a speed of 
one round in 3 J minutes, and an average of one round in 6-J- minutes. 
This continued, gradually diminishing in speed, until the fifth day, 
when two complete rounds were followed, taking 14f and 23 J 
minutes respectively. Shortly after, the palp reached the margin 
of the water, where it remained. 
A specimen from a mud oyster moved upwards, and rotated right- 
handed, but very slightly. During the second and third days it 
moved very little to the right, without any turning, and then 
ceased. 
Palps generally . — When the palps of either side were laid down 
together they rotated in the direction of their cut margins, and 
