62 



ORGANIC DEPENDENCE AND DISEASE 



which has been found encased in a honeycomb coral (Favo- 

 sites) of the Onondaga limestone (Lower Devonian), is ap- 

 parently as completely degenerated as the existing barna- 

 cles. Hercolepas is an acorn barnacle from the Sw^edish 





iiW 









n'f. ^..fW- 



51 



Fig. 51. A Paleozoic barnacle, PaJaeocreusia devonica, buried partly by biirrowing 

 and partly by solution, in a colony of the coral Favosites. Onondaga limestone 

 (Lower Devonian). 



Silurian. The recent discovery by Ruedemann, to which 

 we have referred, of a primitive Balanus in the Ordovician 

 (Lorraine shale) attached to the shell of a cephalopod (En- 

 doceras) and in several stages of its growth, has beautifully 

 indicated the mode in which this degeneration has taken 

 place. In this early species the valves are simple apposed 

 plates, corresponding in size and number on each side, and 

 these, the author cited believes, were developed from free- 

 swimming phyllopods (like the Apus of present waters) of 

 earlier faunas by two factors : 



a. Fixation by the back, so as to give a better play to 

 the feeding and breathing appendages. 



b. Lateral stresses exerted on the long pod-shaped cara- 

 pace, by the play of the currents from without and the re- 

 action from within which eventually developed sutures 

 where these strains were greatest. 



Thus we seem to have traced back to pretty clear indica- 

 tions of its beginning this highly degenerate crustacean, and 



