56 



OEGANIC DEPENDENCE AND DISEASE 



shown by tlie spiral or meandering worm tubes which are 

 fonnd in connection with the glass-sponges Hydnoceras and 

 Prismodictya of the Chemung fauna (Upper Devonian of 

 New York). 



41 



Figs. 41, 42. Two silicious sponges, Hydnoceras and Prismodictya, with mark- 

 ings of worm tubes on the reticulum. Upper Devonian. 



In a considerable number of individuals of Prismodictya 

 from the same locality nearly all showed the presence of 

 the annelid commensal and as the surface of the impres- 

 sion left in the sands by the worm tube is in all cases 

 crossed by the reticulated skeleton of the sponge it is in- 

 ferred that the position of the former was internal. These 



