608 J. E. DUERDEN. 
any part in the swallowing of entire entomostraca, annelids, 
insect larve, and the like which form the ordinary food of 
Hydra; the cilia, however, are certainly capable of such a 
performance in coral polyps and actinians. 
SIGNIFICANCE OF Mucus. 
The foregoing experiments indicate that mucus is an 
important factor in the feeding and other activities of corals. 
As is well known, the outer Jayer or ectoderm in all coral 
polyps is largely made up of unicellular mucous glands, 
separated by long narrow supporting cells, with nematoblasts 
here and there. When detached by maceration and also in 
sections the outer half of the mucous cell is generally found 
filled with a clear transparent fluid, the cytoplasm and 
nucleus having been pressed toward the inner mesogleal 
aspect of the cell; sometimes the contents of the gland cells 
are finely granular, the latter being perhaps a stage in the 
formation of the clear mucus. ‘he mucus usually stains 
intensely in Delafield’s hematoxylin. 
Under ordinary circumstances the exuded mucus forms 
merely a thin layer over the external surface of the polypal 
wall. But when the polyps are irritated, as when roughly 
handled, they send out enormous quantities of the clear, 
viscid secretion, though, on account of its transparency and 
absence of colour, it is not usually perceived; also on 
mechanically irritating certain actinians (Lebrunia) I have 
found the fluid to be exuded to such a degree as to give an 
almost gelatinous consistency to the water in which the 
polyps were contained. 
The experiments with light débris and fine powders have 
shown that when such substances fall upon the polypal sur- 
face they become embedded or entangled in the superficial 
layer of slime, so that the particles are no longer free to move 
independently, but only as a part of the mucous layer. 
Further, the superficial mucus bearing the foreign particles 
