52 OEGANIC DEPENDENCE AND DISEASE 



ent coral. In many cases, such 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 epitheca 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-half 

 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, 

 thev have been buried in the later accumulations of ster- 



