ORGANIC DEPENDENCE AND DISEASE 
59 
Fig. 46. A crinoid stem from the Carboniferous with deep pits over the surface 
which may be due to the work of Myzostomites. 
Fig. 47. Transverse sections of a calcareous hypertrophy or “gall” on the jointed 
stem of a Devonian (Hamilton) crinoid. This shows, by etching and trans- 
parence, the filling of minute worm like tubules in the enlarged stem joints, 
and a darkened aggregate at the center along the stem-canal which has been 
contracted and obstructed by the spread of this growth, producing a genuinely 
pathologic condition. Enlarged. (The specimen from which these sections 
were made presented by Professor George H. Chadwick. ) 
specimen here figured from the Hamilton shales of the De- 
vonian. 
Commensalism of coral with coral. The so-called genus 
Caunopora is an interesting illustration of this habit of 
growth. Caunopora is a compact hydroid coral with sharply 
defined and definitely walled tubes scattered through its 
substance. For a long time it was regarded as the work of 
a single hydroid colony, but it is now known to be a lami- 
nate hydroid overgrowing a series of erect coral tubes like 
those of Syringopora or Aulopora. Fistulipora occiclens 
presents a similar coalition of a hydroid coral growing 
about the tubes of Aulopora. These are both Devonian oc- 
