52 
ORGANIC DEPENDENCE AND DISEASE 
ent coral. In many cases, sncli as that illustrated in figure 
38, the worm tube is directly fixed to the gastropod; 
again it may be free of the gastropod and separated 
from it by the thickened basal covering or epitlieca of the 
coral. With the multiplication of cell growth and the up- 
ward trend of the coral, the worm began its convoluted 
growth, its tube growing as much at one end as at the other 
and with the same curvature at each end. Many of the ex- 
isting tubicolous as well as the boring worms have their 
tubes open at both ends. In view of the regularity of coiling 
shown in some of the commensal worm tubes it is interest- 
ing to notice that in this case the worm, after making a 
start, gets its double coil into parallelism for from one-lialf 
to an entire turn and then each arm starts off into a direct 
course outward and upward following the radial path of 
the coral cells. These tubes often pass in and out between 
the cells, shut off from them by secretions of the coral sub- 
stance, keeping their extremities always at the tentacular 
surface, and very seldom is there evidence of the worm 
encroaching on the polypite cells. Still this may occur and 
the worm tube occasionally becomes encased by a young 
polypite and holds a position in the center of the cell. Not 
always does the growth of coral and polyp and worm go 
on pari passu. In a group of the largest specimens of these 
corallites we have seen, taken from the shales on Jaycox’s 
run, Genesee county, N. Y., the later and accelerated growth 
of the polyps seems to have overwhelmed and strangled the 
worms whose tubes continue halfway or more upward and 
then abruptly end. 
Other worms also may be encased in the thickening base 
of the growing coral, as shown in figure 30, but it is not 
yet clear where their apertures lie, as I have never seen 
more than two annelid openings at the surface of an adult 
coral, both belonging to the same tube. Originally opening 
on the tentacular surface at an early stage of coral growth, 
they have been buried in the later accumulations of ster- 
