ORGANIC DEPENDENCE AND DISEASE 



61 



Fig. 50. A colony of the coral Farosites nicujarens'is which has partially overgrown 

 a small plantation of the eyathophylloid coral Amplexns. From the Niagara 

 formation (Silurian), Montieello, Iowa, x y^. 



THE BARNACLES 



It is well known that the barnacles are degenerate and 

 attached crustaceans. The acorn barnacle with its hard 

 valves consolidated into a cone-shaped shell, and the goose 

 barnacle Avith its flat shells on clustered stems, represent 

 for us the living members of this interesting group of 

 recreants/ In the barnacle, of whichever kind, the animal 

 has lost its independence through attachment by its head 

 or back and the readjustment of its segmental plates to fit 

 the demands of its stationary maturity. Ontogeny shows 

 a free and normal larval state for the barnacle and indi- 

 cates a phylogeny in which locomotive independence had 

 been normal throughout life. 



We have known for some years the existence of barnacles 

 in the Paleozoic rocks. The acorn barnacle Palaeocreusia, 



1 Far greater degeneration of anatomy and function is presented by several 

 other forms of soft-bodied barnacles in existing seas. 



