42 



ORGANIC DEPENDENCE AND DISEASE 



Silurian. The reef-building coralloids, Stromatopora, 

 which abound in the stages of the Silurian are frequently 

 permeated with straight tubes of the worm Gitonia sipho. 

 This is an occurrence often repeated in the Stromatoporas 

 and true corals (Favosites) of the Lower Devonian. 



Devonian. Interesting simple combinations of this cate- 

 gory are shown by individual polyps of cyathophylloid 

 corals like Zaphrentis and Cyathophyllum, where we have 

 frequent indication that the tube of the worm is open at 

 both ends and its continuity unbroken, each end opening 

 at the tentacular surface of the coral. Often the worm dies 

 in the coral and is buried in the stereom, or its upward 

 growth is not so rapid as that of the coral and it is left be- 

 hind with its head protruding from the side of the corallite. 

 It is also quite evident that the coral may so build its tissue 

 about the worm as to inclose it in a sheath which takes the 



Fig. 8. Head of the trilobite Dalmanites overgrown by a colony of the bryozoan 



Montieulipora in which is embedded a series of the tubes Gitonia sipJio. Onon- 



daga limestone (Lower Devonian). 

 Fig. 9. Colony of the coral Favosites sphaericus with a series of Gitonia tubes. 



Helderbergian (Lower Devonian). 

 Figs. 10, 11. A weathered surface and a transverse section of a Stromatopora 



full of Gitonia tubes. Cobleskill (Upper Silurian). 



