THE ROLE OF MUCUS IN CORALS. 593 
rather quickly over the sides of the polyp, the others settling 
upon the surface (fig. 1), while if the mouth be closed they 
all drop upon the dise and there come to rest. The particles 
which fall on the polyp are afterwards no longer free to move 
independently ; even astrong stream of water from a pipette is 
unable to dislodge them. 
It is evident that on settling the foreign particles become 
embedded in a layer of mucus covering the polypal surface, 
for by means of a camel’s hair brush or a stream of water 
from a pipette a layer of this character can be detached in 
shreds, and in it are contained the objects which have fallen 
upon the polyp. Moreover, if the débris be allowed to 
remain undisturbed for a time, and the polyp should open its 
mouth, a mucous layer is detached by the activities of the 
polyp itself, and is soon broken up into shreds and patches, 
which are then moved slowly towards the edge of the disc, 
over which they fall to the bottom of the vessel. After 
removal of the mucus the surface of the polyp is perfectly 
clean and free from foreign particles. 
Likewise if carmine or sepia mixed in sea-water be allowed 
to fall upon the disc the coloured particles are somewhat 
uniformly distributed as they slowly settle in the mucus, and 
will remain thus for several minutes or even hours if the 
mouth remain closed. Ultimately, when the mouth is opened, 
the layer of mucus containing the particles becomes broken 
up and arranged in more or less radial strands and shreds, 
which are slowly transferred to the margin. Very rarely the 
coloured shreds are drawn in the reverse direction, that is, 
towards the mouth, and are then ingested. 
When, instead of non-nutritive particles a filtered nutritive 
solution, such as meat or crab extract, is discharged over 
the disc of Fungia, a series of very decided responses are 
observed :—(1) The tentacles begin to move about freely, 
their inclination being mainly towards the mouth; (2) the 
disc is partly retracted upon the skeleton; (3) the mouth 
opens widely, and the solution can be seen passing from the 
disc down the stomodzeum, an inhalent current having been 
