230 EVENINGS AT THE MICROSCOPE 



toward the sessile Barnacle enclosed in its shelly cone of 

 several valves, and firmly fixed to the solid rock; and we 

 are yet at a loss to imagine how such a change can be 

 effected. 



Nor is the matter apparently helped by the next moult; 

 for though there now ensues a great change of form, it 

 does not seem to resemble the adult Barnacle much (if 

 at all) more than before. If described without reference 

 to its parentage, it would still be considered an Entomos- 

 tracous Crustacean, or Water-flea, but removed to another 

 tribe. It represents, in fact, a Cypris; 1 the body with 

 its fringed limbs being now included within two convex 

 valves, like those of a mussel or other bivalve shell, either 

 united by a hinge along the back, or rather soldered to- 

 gether there, so as only to allow a slight opening and 

 closing by the elasticity of their substance. The fore part 

 of the head is now greatly enlarged, as are also the an- 

 tennae, which project from the shell. The single eye is 

 separated into two, which are large and attached to the 

 outer arms of two bent processes which are placed within 

 the body, in the form of the letters UU- The legs are in- 

 creased by the addition of two pairs, and these are doubly 

 bent in a zig-zag form, and can be protruded from between 

 the valves. 



It is a highly curious fact that the infant Barnacle has 

 thus passed through two distinct types of animal life, the 

 Cyclops and the Cypris. These are not one type in differ- 

 ent stages, as might be reasonably presumed. The young 

 of Daphnia and of Cyclops are so much alike that it would 

 be natural to presume the young of Cypris to be of the 



1 See figure on page 210. 



