375 



CHAPTEE XXL 



CRUSTACEANS. 



Cirripedes Barnacles and Acorn-shells Edriophthalmia Decapoda Their 

 Branchial Apparatus Legs and Digestive Organs Moulting Process Meta- 

 morphoses Enemies of the Crustaceans Means of Defence, and Offensive 

 Weapons The Birgus Pinnotheres Paguri Migratory Instinct, of the Land- 

 crabs. 



Barnacle, 



As the dry land teems with infinite forms of insects, so the seas, 

 from the equator to the poles, are peopled with legions of crus- 

 taceans. Though all constructed on the same fundamental 

 plan, yet the various 

 subdivisions of this vast 

 and important class differ 

 so much in outward ap- 

 pearance, and their or- 

 ganization is so consi- 

 derably modified according to their various habits, that even 

 the eye of science has been long unable to distinguish the real 

 nature of several of their lowest forms. 

 Thus the Barnacles, which frequently 

 attach themselves in such vast numbers 

 to ships' bottoms as materially to ob- 

 struct their way, and the Acorn-shells, 

 which cover in scurfy patches the sur- 

 face of exposed rocks, often lining the 

 coast for miles and miles, were formerly 

 reckoned among the molluscs, until a 

 better knowledge of their early stages 

 of development proved them to be real 

 crustaceans, distant relations of the crab or lobster, whom when 

 full-grown they so little resemble. 



While in the first stage of infancy, these ambiguous creatures 



Acorn- shell, 



*a first series of compartments, 

 b second series, c cirri. 



