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596 Annelid Messmates with a Coral. [June, 
which it is attached. The young of M. fragile is a simple fungia- 
like’ coral attached at its base, somewhat cup-shaped, with smooth 
outer walls. As it grows older new individuals form as buds, 
upon the upper part of the disk in circles about the original and 
centrally placed polyp. 
These buds differ somewhat from the parent, and as in the branch- 
ing Madrepore, Madrepora cervicornis, we have two kinds of indi- 
‘viduals, a single large—the original polyp—and several smaller 
found below it on the sides of the branch; so in the saucer-shaped 
colonies of Mycedium there are, as is best seen in smaller colo- 
nies, an original polyp, found in the center of the disk on its uppèt 
side, and smaller, or buds from the same, which are arranged in 
regular concentric circles about it. The smooth under side of the 
Mycedium is destitute of coral individuals, and is generally cov- 
ered with Bryozoa, small mollusks and worms ; of the latter one 
of the most interesting is the tubicolous annelid which is claimed 
as a messmate of the coral, and is thought of more importanc 
than the rest in the determination of the ultimate form of the 
growing coral community. 
The calcareous tube in which the worm lives is firm . 
throughout most of its length to the under side of the coral. Its 
terminal opening in a Mycedium of regular shape, lies near the 
rim of the saucer-like disk of the young coral. In the growth 
of the rim this extremity of the worm tube is imprisoned by the 
increasing edge of the disk in such a way that it is wholly suf- 
rounded by the live coral in the progress of its growth. 
growth of the worm tube, however, keeps pace with the ye 
of the coral about it, and as it rises above the upper eni 
the Mycedium the opening into the tube is kept uncovered 
this growth, so that the head of the annelid with its ge 
branchiz can always have free communication with the avi ; 
water, notwithstanding the tube itself is often wholly enclosed i 
the calcareous secretions of the polyps. When the growing i 
covers the terminal opening of the worm-tube the vom 
but this rarely occurs, as the closing of the opening 15 poe i 
prevented by a corresponding growth of the tube. © ‘a 
specimens examined the extremity of the tube had we A 
direction at right angles to the upper surface of the cor 4 
ly united 
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ungia that 
1 The resemblance is closer to the attached young (“ Strobila ”) om 
to the free adult. 
