CIRRIPEDIA. 



161 



of a sub-elliptic form, slightly compressed, and of a brownish tint : 

 the body of each was defended by a shell composed of two valves, 

 joined by a hinge along the back, and opening along the opposite mar- 

 gin for the protrusion of a large and strong anterior pair of limbs (^ar), 

 provided with an adhesive sucker and hooks, and of six pairs of pos- 

 terior jointed members (b), terminated by a pencil of bristles. These 

 natatory limbs acted in concert, so as to cause the animal to swim 

 by a succession of bounds like the water-fleas (^Daphnia). The 

 body was terminated by a short tail (c), composed of two setigerous 

 joints. A pair of pedunculated compound eyes («-/) was attached to 

 the anterior and lateral part of the body. Other specimens of this 

 little seeming crustaceous animal were taken on the first of May and 

 preserved alive in a glass vessel of sea-water. On the night of the 

 eighth two of them had thrown off their outer skin, and were firmly 

 adhering to the bottom of the vessel, where they rapidly assumed the 

 form of the young of the sessile Barnacle called Balarius pusillus. 

 The sutures between the valves of the shell and of the operculum 

 were visible, and the arms, though not yet perfectly developed, were 

 seen moving within. The eyes also were still perceptible, although 

 the principal part of the black colouring matter appeared to have been 

 thrown off" with the exuvium. On the tenth of May another indi- 

 vidual was seen in the act of throwing off" its exuvium and attaching 



itself to the bottom of the 

 glass. As the calcification of 

 the shell proceeds, the eyes 

 gradually disappear and the 

 visual ray is extinguished for 

 the remainder of the animal's 

 life. The arms at the same 

 time acquire their usual ciliated 

 structure. 



The Lepas, in its transitory 

 locomotive stage (^^.88.), does 

 not, like the young Balani, re- 

 semble the bivalve Ostracoda, 

 but rather approximates to the 

 genus Cyclops* It has a single 

 median sessile eye-speck (rf) ; 

 three pairs of members, the 

 most anterior of which {a, a,) 

 Young Lepas. are simple, the others (6, b,) 



* See Mr. Thompson's Memoir, Philos. Trans. 1835. 



