ORGANIC DEPENDENCE AND DISEASE 41 
cially with the corals and the sponges and the calcareous 
algae. 
The coexistence of the tubicolous worms with the corals 
is one of the commonest phenomena of present seas and it 
became established as early as the Silurian. In most of 
the ancient cases observed it is an elementary expression 
of commensalism, but not long after its start it becomes at 
times rather complex. Worm and coral may start together 
directly on settling down from the free larval state, or con- 
junction may be formed by attachment of the annelid larva 
after the growth of the coral has well progressed. In both 
cases the growth of the latter engulfs the former save at 
its tentacled aperture. We give herewith examples of these 
occurrences . 1 
Fig. 3. The coral Cystiphyllum with short tubes of Gitonia corallophila opening 
outward through the thecal walls. 
Fig. 4. A calyx of Zaphrentis with a number of tube openings of Gitonia. 
Figs. 5, 6. A Zaphrentis from two points of view to show the course of the tube 
of G. corallophila with both ends opening outward into the calyx. 
Fig. 7. Tubes of this character opening through the lateral walls of Zaphrentis. 
All are from the Onondaga limestone (Lower Devonian). 
i Some of these illustrations are taken from the writer’s “ Beginnings of 
Dependent Life” (1908), but to these and to the other classes discussed, new 
illustrations have been added. 
