ORGANIC DEPENDENCE AND DISEx\SE 



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. Chad wick. ) 



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 occidens 

 presents a similar coalition of a hydroid coral growing 

 about the tubes of Aulopora. These are both Devonian oc- 



