142 
ANIMAL LIFE ON THE 
see arise the little golden darts. But continuing our observa- 
tions, we notice the foot has other peculiarities. Here we 
see a portion of it rising into a little insular height ; on the 
other side we notice an opposing indentation. There it 
cuts into a ridge, here into a hollow; and all over its 
surface it twists and contorts itself into all sorts of incon- 
ceivable shapes and positions. Place it again in the water 
in a position to adhere and we observe the same contortions. 
The high portions are adhering to the glass, while the lower 
ones are not. Press the shell down with the finger, and 
though there is at first a very little slip, we instantly feel 
the resistance of the adhesion. Nevertheless the contortions 
in the foot remain the same, and continue in that condition 
until the creature finds it convenient to change its position. 
Under these circumstances, we see that adhesion is not 
due to a vacuum of the whole foot, and we think we may 
also safely infer that the glue theory is not the correct one. 
If the force of resistance depended upon glue, then there has 
been, on the part of the Maker, an unnecessary expenditure 
of muscle-power in this creature — a circumstance that never 
occurs ; and we know that in the case of the bivalves the 
muscles are the only source of resistance against opening. 
My opinion, therefore, is that the sole of the foot of the 
limpet is a living mass of minute sucker organs, each one 
capable of forming a vacuum in itself ; and were the whole 
foot cut into sections while on its place on the rock, each 
section would be capable of retaining its hold, while the 
muscles above possessed their tension power to draw them 
up. In the foot of all the top families the same law of strong 
adhesion is observable ; and the presence only of these two 
specimens in such numbers here is a verification of Nature's 
inexorable law of the "survival of the fittest;'' for amongst 
the migratory tribes of the shore few others can be found 
