THE ROLE OF MUCUS IN CORALS. 611 
shortly after exudation. When freshly secreted, as from 
stimuli of nutritive juices, it is a clear, colorless, watery, 
viscous fluid, readily forming into separate streams; but 
after an exposure on the disc or tentacles for some time the 
superficial layer becomes more consistent, more membrane- 
like, and is then capable of being separated only in patches 
or shreds. In actinians where the mucus is rarely shed, as 
in Phellia and Adamsia, it forms a more or less permanent 
membranous coating. Such physical changes are well known 
in the mucus exuded by other organisms, such as molluscs 
and planarians. In these the secretion is also very thin or 
watery when first secreted, but rapidly changes so as to 
become more consistent. 
The separation of the exuded mucus from the discal and 
tentacular surfaces in the form of patches or shreds is de- 
pendent upon the stomodeeal currents, probably influenced by 
the movements of the disc and tentacles. If the mouth be 
closed and no incurrent or excurrent is produced the matted 
mucus simply remains upon the disc, may be for hours or 
days. In the forms studied there was no evidence of ciliation 
over any external part of the polypal surface such as could 
effect or assist in the removal... When, however, a stream of 
water from the stomodeum, or even from a pipette, was 
forced over the disc, either outwardly or inwardly, the 
mucus was detached from its adherence to the polypal 
surface and broken up into irregular patches, and then either 
drawn inwards or wafted outwards according to the direction 
of the current. By the action of the outward currents the 
mucous patches are often rolled into boli and then dropped 
over the sides, whereas when drawn into the stomodzum the 
mucus is in the form of distinct continuous streams. When- 
ever indrawal takes place as a result of external stimuli there 
ig an accompanying increase in the secretion of mucus. The 
peripheral movement is a wafting or floating away of detached 
strands or patches, the centripetal is an indrawal of several 
watery streams. 
- Not only does the mucus serve as a protection to the polyp 
