726 Proceedings of Royal Society of Edinburgh. [sess. 
"being relatively the weaker, — the right moving at an average rate 
of about one round in about 1 4 minutes, and continuing for about 
10 days,' the left moving considerably more slowly, and continuing 
for over 7 days. 
3. Outer Palps . — The right is very fitful in its movement, and 
varies considerably in different cases, both as regards rate of move- 
ment and direction of rotation ; but the typical specimen rotates 
slowly left-handed, at an average rate of one round in 8f minutes ; 
this movement going on for 52 hours, the rate of rotation 
diminishing gradually to one round in 3 hours and 10 minutes. 
The left invariably rotates right-handed, and the average rate was 
one round in 5 minutes. 
4. Labial Palps generally .— The palps, normally, rotate inwards 
or towards their attached margin, and both on the same side rotate 
in the same direction. In some cases abnormal rotation occurs 
away from the attached margin. The rate varies from 5 minutes to 
14J minutes per round. The two outer palps seem to he possessed 
of nearly equal motive power, while of the two inner, the right is 
relatively twice as powerful as the left. The duration of movement 
is usually about a week, hut the right inner continued for 10 days. 
It must be remembered, however, that when visible or even micro- 
scopic movement of the palp has ceased, the cilia are still in active 
motion. 
The constancy of direction of the palps was well maintained. 
The right inner and left outer never varied from their normal. 
The right outer, in four recorded specimens, rotated in its normal 
left-handed direction, hut one of them (the first too) began right- 
handed. The left inner also rotated normally right-handed in four 
specimens, hut one of them on the fifth day was found moving in the 
reversed direction. 
It would he interesting to determine how far the rotation of the 
palps of the Swan Anodon of Britain (Anodonta cygnea) agrees 
with the above. 
II. Gills. — The entire right outer gill moves extremely slowly in 
the direction of its cut surface ( J inch in 5 days), and there is slight 
rotation of the anterior end. There is no movement of the left gill 
at all. A piece of the left inner gill in one case exhibited slight 
forward movement (1 inch in 24 hours), a second moved forwards 
