METAMORPHOSIS OF CIRRHIPEDS. 



647 



study of which has contributed most essentially to the elucidation 

 of their real nature. The observations of Mr. J. V. Thompson,* 

 with the extensions and rectifications which they have subsequently 



Fig. 332. 



Development of Balanus balanoides : — a., earliest form ; — b, 

 Larva after second moult ;— c, side view of the same ; — d, stage 

 immediately preceding the loss of activity; a, Stomach (?) ; 6, 

 Nucleus of future attachment (?). 



received from others, show that there is no essential difference be- 

 tween the early forms of the Sessile (Balanida?, or ' Acorn-shells') 

 and of the Pedunculated Cirrhipeds (Lepadidse or 'Barnacles'); 

 for that both are active little animals (Fig. 332, a), possessing 

 three pairs of Legs and a pair of Compound Eyes, and having the 

 body covered with an expanded Carapace, like that of many Ento- 

 mostracous Crustaceans, so as in no essential particular to differ 

 from the Larva of Cyclops (Fig. 331, c). After going through a 

 series of Metamorphoses, one stage of which is represented in 

 Fig. 332, b, c, these Larvae come to present a form, D, which 

 reminds us strongly of that of Daphnia ; the body being enclosed 

 in a Shell composed of two Valves, which are united along the 

 back, whilst they are free along their lower margin, where they 



* "Zoological Researches," No. in., 1830. 



