OUR CAECINOLOGICAL FRIENDS. 105 



serve to carry the necessary nutritive particles to 

 the mouth. 



As we find it in its adult condition the harnaele 

 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 antennae, 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 



