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 cyathopliylloid 
corals like Zaplirentis 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 
Monticulipora in which is embedded a series of the tubes Gitonia sq)lto. Onon- 
daga limestone (Lower Devonian). 
Fig. 9. Colony of the coral Favosites spliaericus with a series of Gitonia tubes. 
Helderbergian (Lower Devonian). 
Figs. 10 7 11. A weathered surface and a transverse section of a Stromatopora 
full of Gitonia tubes. Cobleskill (Upper Silurian). 
