OUR CARCINOLOGICAL FRIENDS. 105 
serve to carry the necessary nutritive particles to 
the mouth. : 
As we find it in its adult condition the barnacle 
is a much altered or metamorphosed animal, wholly 
unlike what it was before it became attached. In 
its earlier stage it is a free-swimming, active creat- 
ure, with well-developed legs and a hinged bivalve 
shell, on the whole much like some of our so- 
called fresh-water fleas (Cypris). But it soon fixes 
itself by means of suckers developed upon the 
first pair of antenne, exudes a slimy substance 
which helps to make the stalk, and thus, head 
downward, passes through those subsequent met- 
amorphoses which lead up to the mature animal 
and almost completely mask its true character. 
Indeed, until within a comparatively few years the 
barnacles were classed with the mollusks, even the 
great Cuvier mistaking their affinities. 
It might naturally be supposed that an animal 
so tightly closed up in its shell as is the barnacle 
would have little use for organs of vision, and that 
accordingly these organs would be found wanting. 
But careful investigation of the tissues has revealed 
the presence of a single eye-speck, of a duplex 
origin, not far from the region of the mouth, which, 
though thus deeply hidden within the shell, still 
permits the animal to distinguish at least between 
light and darkness. Allow your hand to pass over 
a pan of sea-water containing barnacles, and ob- 
serve by their actions how readily the animals dis- 
tinguish between the different intensities of light. 
Several species of stalked-barnacles are found on 
