56 
ORGANIC DEPENDENCE AND DISEASE 
shown by the spiral or meandering* worm tubes which are 
found in connection with the glass-sponges Hydnoceras and 
Prismodictya of the Chemung fauna (Upper Devonian of 
New \ T ork). 
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 
