SHORES OF THE CLYDE AND FIRTH. 
77 
round their entire circumference, lie the mantles on which 
are set on a fleshy ground a row of little beads shining 
with the colour and brightness of little emeralds, receiving 
the effulgence of their beauty from a hidden light within. 
These are the creature's eyes, and it is only now after 
recovering from the wonderment of such beauty we begin 
to observe the construction and uses of the organs before 
us. The mantles are composed of fibrous tissues that run 
round the entire shell to the hinge where they are attached 
to the body of the creature near the mouth. The work 
they perform is, in the first place, to protect the delicate 
interior, and act as a rudder in steering the creature along 
its erratic course, by ejecting the water at any point re- 
quired, and again to throw out whatever extraneous matter 
may happen to be drawn in. 
It is a fine sight to witness this operation performed. 
Looking at the mantles when lying inward a little, both 
appear like two attached webs, rising and falling in an 
angular fashion, but in reality each one is an entire organ, 
capable of being wrought from the centre like a hinged 
flap. Between the rows of eyes a double line of tentacles 
are seen protruding on the outer edge, some of which are 
double the size of the others ; and on the inner edge these 
tentacles are again seen, but at this point they are smaller 
than the others. In watching the movements of these 
tentacles, they will be seen to suddenly start inward and 
grow considerably less in bulk and length, when instantly 
the inner half of the mantle makes an eccentric movement, 
and that portion coming out with a swing, sends the watery 
refuse beyond the lips with a dash. Between the sinking 
of the tentacles and the movement of the flap there is about 
a moment of a pause, so that this seems a pretty certain 
sign that the tentacles are wrought from the extremities by 
