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 Swedish 
51 
Fig. 51. A Paleozoic barnacle, Palaeocreusia devonica, buried partly by burrowing 
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 ceplialopod (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 pliyllopods (like the Apns 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-sliaped 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 
