THR ROLE OF MUCUS IN CORALS. 605 
mouths of the surrounding individuals, as shown in fig. 6. 
Manifestly under such circumstances any single mucous 
strand is pulled at from both extremities, and as the indrawal 
continues it reaches in time a state of tension. The strands 
are then seen to break or divide about the middle, and each 
moiety passes to its own polyp and is ingested. Evidently 
upon stimulation by nutritive juices the mucus in Favia is 
exuded in such quantity as to form a continuous superficial 
layer over the colony, and to bridge the intervals between 
adjacent polyps. 
Fic. 6.—Several polyps of Favia showing the distribution of 
nutrient particles after falling upon the colony. ‘The particles are 
becoming arranged in mucous streams and drawn down the sto- 
moda. Frequently the streams passing down the mouths of 
adjacent polyps are continuous. 
The polyps of Favia very readily respond to the influence 
of nutritive juices, and many experiments can be arranged to 
illustrate the quickness with which the reversal of the dominant 
movement of the stomodeal cilia takes place. If when non- 
nutritive particles of carmine, sepia, or talcum powder are 
being wafted outwards towards the polypal margin a solution 
of meat extract is dropped upon a colony the outward move- 
ment at once ceases, a momentary rest occurs, and then a 
reversal in the direction of motion takes place. The mouth 
is widely opened and streams of mucus are indrawn, carrying 
