THE ROLE OF MUCUS IN CORALS. 613 
without doubt influenced by the envelope of mucus gathered 
in the struggles of the organism, the secretion of the mucus 
being much increased by the mechanical and chemical stimuli. 
Itis probable that all food before ingestion becomes enveloped 
in mucus. 
An interesting case illustrating the protective value of 
mucus under adverse conditions occurred in the course of the 
investigations. Colonies of Porites living in the tanks in 
which were kept other corals used in the experiments appar- 
ently found the conditions unfavourable, and the polyps be- 
came wholly retracted and inactive. ‘To all appearances the 
polyps were dead, and fine particles of mud and débris from 
the somewhat cloudy water settled upon the colonies. How- 
ever, having transferred the colonies to other and apparently 
more favourable conditions the polyps, after a time, began to 
expand, when it was found that they had to break through a 
rather dense felt of mucus and foreign particles, which had 
formed over the entire surface during the several days of 
inactivity. For some time the colony presented a ragged 
appearance, that is until all the mucous shreds and patches had 
by one means or another been removed. It is manifest that 
by forming such a coat of mucus, coral polyps have a certain 
power of protecting themselves during periods of inactivity, 
whether brought about by slight changes in the composition 
of the water, muddy conditions, or variations in temperature 
SUMMARY. 
1. Under ordinary conditions the outer surface of coral 
polyps is covered with a thin, continuous layer of mucus, in 
which objects falling upon the polyp become embedded or 
entangled. 
2. When first exuded the mucus is thin and watery, but 
later becomes more consistent. From time to time itis broken 
up into shreds and patches which are driven or wafted from 
the surface of the disc by the ordinary exhalent currents from 
VOL, 49, PART 4,—NEW SERIES. 45 
