MARINE ARTHROPODS 



263 



. The Acorn Barnacles, so numerous on our shores, are good 

 types of the Cirripedia, and they are so easily kept alive in the 



FIG. 193. A CLUSTER OF ACORN SHELLS 



indoor aquarium that their interesting movements may be well 

 observed. A cluster of these animals may be obtained by chipping 

 off a piece of the rock en which they grow ; or, instead of this, a 

 few minutes' searching on 

 a rocky coast at low tide 

 will certainly provide us 

 with a stone of suitable 

 size, or the shell of a mol- 

 lusc, on which the crea- 

 tures have found a home. 

 Place them in the 

 indoor aquarium, or in 

 any shallow vessel con- 

 taining just sufficient sea- 

 water to cover them, and 

 carry out your observa- 

 tions with the aid of a 

 hand lens. They will soon 

 open the inner cone of their many-valved shell, and slowly pro- 

 trude six pairs of gracefully curved and delicately-feathered ap- 

 pendages which, as previously stated, are attached to the thoracic 



FIG. 194. SHELL OF ACORN BARNACLE 

 (Balanus) 



