SHORES OF THE CLYDE AND FIRTH. 101 
possession, pierced by, at least, six holes, I find they 
measure, on an average, an eighth and sixteenth of an inch 
at the top and half an inch at the bottom, through two 
inches of stone. In such a position, were the syphons 
distended by water, as described in this theory, and the 
tube partly exposed, as of necessity it would have to be, it 
would become swollen beyond its normal size, and, conse- 
quently, would press in the inside against the tapering hole, 
and in the outside against the outlet; and the top of the 
tube being closed, the consequence would be that the 
creature's effort would stultify itself by the swollen tube 
blocking up the passage. The fact of the passage being 
lined with fine particles of mud is no proof of the correct- 
ness of the theory. During the course of my observations 
I have noticed the mantle coming out with a sudden splash, 
and send the particles in the water dancing round, and this 
I believe to be partly the cause of the mud deposits in the 
passage. However, it must be borne in mind that the 
syphon tube, being lined at the base by a coarse epidermis 
or skin, is quite liable to gather mud on the outside, and, 
of course, it will be carried with it to the inside, and there 
deposited. But the field of observation is free, let us enter 
it also. Examining the foot then minutely, we neither can 
find any trace of an orifice ; but splitting it open at the base, 
out pops a round, gristly, water-coloured membrane, beetle- 
shaped at the base, but rounding to a point at the upper 
end. This is a distinct membrane with no seeming point of 
attachment to any other part of the body ; but what its 
work is I have not yet been able to learn. At first sight, 
its shape suggests the idea of a spile or stopper for some 
internal valve leading from the supposed orifice ; but while 
the base of the foot is fibrous enough, the upper portion 
takes the shape and consistency of that organ in other 
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