1888 .] 
Mr D. Alpine on Bivalve Molluscs. 
185 
The right outer palp behaves in a similar manner, and the general 
results were confirmed by other series of observations. The labial 
palps immersed in water have the power of moving in the direction 
of the cut end, and in one case a left labial palp moved 9 inches 
in 22 minutes ; 36 inches were covered in 82 minutes, one 9-incb 
section taking only 16 minutes. The labial palp has also the power 
of turning itself from side to side, and could creep along on one 
margin. 
Duration of Independent Movement of Palps when kept moistened 
ivith Sea-Water . — At the end of seven days the palps of the sea- 
mussel reacted to stimulation ; those of the fresh-water mussel (Unio) 
reacted at the end of eight days. They rotated in both directions ; 
the outer palps rotating outwards, the inner normally inwards. It 
should be noted that the ridged and transversely striped exterior 
surface of the inner palp corresponds to the interior surface of the 
outer palp, the smooth outer surfaces of the one again correspond- 
ing to the inner surface of the others. 
Gills — Description . — The gills are attached, on either side to the 
body-wall, and posteriorly by their pointed ends to the dark brown 
tentacular margin of the mantle-lobes. There are a pair of gills on 
each side of the body, the outer next the mantle and the inner next 
the body, and both are about equal in size. No deficiencies have 
been met with here, as in the labial palps. Each gill further con- 
sists of two lamellae, and in the case of the inner gill, as seen from 
the inner surface, the inner lamella, at the margin next to the body, 
is a thick unattached border, while the other is fixed. There is a 
small space between the two lamellae, interrupted by delicate bands 
stretching obliquely across, and appearing on the surface of the gill 
as dark brown streaks. Hence each pair of gills in transverse 
section has the appearance of a W, the two outer free legs repre- 
senting the outer and inner lamellae of the outer and inner gill, 
while the two united legs represent the other two lamellae. 
The inner gills, drawn and experimented with, were detached just 
along the thickened free border of the inner lamella (fig. 3). The 
gills will be named as in the following scheme ; — 
