90 
ORGANIC DEPENDENCE AND DISEASE 
74 75 
Figs. 74, 75. The perforating sponge Topsentia devonica in a Middle Devonian 
Stromatopora (Iowa). Fig. 74 is a polished section; Fig. 75 shows the embedded 
sponge by transmitted light. 
these made by the worms are in contrast to the perforating 
tubes described because of their usual simplicity and their 
greater size, and among the fossil occurrences these fea- 
tures lead to comparatively easy and safe recognition. 
These simple worm-borings are found in many sorts of 
solid calcareous organic masses in the Paleozoic rocks. 
While we find in the Ordovician worms growing concur- 
rently with solid corals or coralloid bryozoa, like Praso- 
pora, there is no present evidence of perforating worms 
boring into such masses and more specially into molluscan 
and other lieavv shells, until late in the Silurian, from which 
date they acquire greater abundance and in the Devonian 
faunas become widespread. As the evidence now stands 
they were rife in the early Devonian everywhere, even in 
the austral faunas of this period which are in many respects 
widely distinct from the contemporary faunas of the north . 1 
i See Clarke : ‘ ‘ Fosseis Devonianos. ’ ’ 
