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TA hea T S E E S ee DE NA A E T E CEE 
1883.] Anneiid Messmates with a Coral. 597 
projects a full half inch above that plane. The coral, however, 
has formed “ @guo pede” along the sides of this projection and has 
covered it to the very apex. The result is the formation of vari- 
ations in the regular, growth of the coral which may be likened 
to a coral-gall such as is formed by the crustacean genera, Hapa- 
locarcinus, Cryptochirus and others. The greater part of the 
worm-tube lies in sight on the under side of the Mycedium, while 
its terminal opening is almost wholly concealed, being surrounded 
by the live coral community through which there is, however, a 
small opening into the tube cavity inhabited by the worm. 
It is interesting to notice, however, that the modifications in 
form of the growing Mycedium always begin on its rim in the 
Vicinity of the tube opening. As the growth of the coral goes 
on, the portion of the ccenosarc on the edge of the saucer-like 
disk coalesces around the obstruction caused by the tube in 
such a manner as eventually to completely surround it. When 
this has taken place the end of the worm-tube grows upward and 
seems to rise out of the midst of the growing coral. In all cases, 
however, the shape of the coral is changed by the obstruction to 
its otherwise regular growth. 
In Porites and several other genera we have a similar commen- 
salism of annelids and corals. Specimens of P. astreoides in 
which these worm-tubes can be well seen, is found in almost 
every collection of corals. Many specimens have the interior of the 
Coral mass riddled with these worm-cases, whose openings cover 
the Surface of the coral “head.” Such a combination of grow- 
Ng coral and annelids, when both are alive, presents one of the 
most beautiful sights upon a live coral bank. 
_ While younger specimens of Mycedium, almost without excep- 
tion, have a regular disk-like shape, which in older and larger 
Colonies Where the annelid is not found, is still preserved, it al- 
a always happens that the presence of the worm-tube leads 
irregularity in form in the animal upon which it is found. 
Younger Specimens are especially well adapted for a study of this 
Phenomenon, Mycedium grows to the level of low water, and is 
often exposed to the air by very low tides. It is, however, quite 
hardy, and the short exposures are by no means always fatal. It 
Prefers for its home sheltered lagoons to the open reefs beaten by 
ies » Which would soon destroy its fragile disk. Its favorite 
itat is the side of submarine cliffs and caves. 
