DEPARTMENT OF MARINE BIOLOGY l6l 



All the 16 species of corals investigated with reference to ridding their 

 surface of non-nutrient particles can clean their surfaces. Fine sand grains 

 were used in making the experiments. Some of the sand which may fall near 

 a mouth may at first be swallowed, but soon it will be ejected and the cilia 

 will beat outward, moving the grains, embedded in mucus, toward the 

 periphery. The capacity of corals for cleaning themselves varies from 

 species to species. The special adaptation for withstanding considerable 

 quantities of silt can here only be mentioned. One of them is the capacity 

 through the combined action of the mucus and cilia to remove silt from 

 their surfaces ; another is by having a branching growth form to present no 

 flat surface on which silt may settle. 



Numerous observations and experiments were made to ascertain the nature 

 of the food of corals. While at Golding Cay, Bahamas, Dr. Mayer called 

 my attention to some of the corals kept in a live-car, and also to some in a 

 state of nature, catching and holding specimens of the small jelly-fish (Li- 

 nuche). Subsequently, I saw other instances of similar capture of Linuche. 

 Dendrogyra cylindrus, Mceandra clivosa, and Siderastrea sidera were the cor- 

 als observed that had caught jelly-fish. I have seen a specimen of Mceandra 

 areolata that had caught a small crab, and it digested all the soft parts of the 

 crab. That corals will eat a variety of cut-up animal sea-food, Crustacea, 

 and fish, my feeding experiments proved, and Mceandra areolata will eat 

 pieces of the flesh of its own species. Plankton tows were made and the 

 plankton fed to the corals. Mceandra areolata took copepods, amphipods, 

 crab zoea, Sagitta, Salpa domestica, young fish, etc. ; every kind of visible 

 animal plankton except pycnogonids. The surety and rapidity with which 

 the tentacles worked in catching living copepods was astounding. Of a 

 number of copepods dropped with a pipette within the rows of tentacles not 

 one escaped. Not only did the tentacles catch copepods, but specimens of 

 these small Crustacea dropped on the edge-zone, outside the tentacles, were 

 caught, entangled in mucus, and carried to the mouths. The experiment was 

 tried four times, each time with the same result. Animal plankton was fed 

 to other species and was generally taken. 



Feeding diatoms and chopped-up sea-weeds was tried. The diatoms were 

 obtained from cultures made in the laboratory, as this method gave an abun- 

 dance of these organisms with only a small admixture of other kinds. Not 

 a coral experimented with would take pure diatoms as food, but would take 

 them if they had been soaked in meat-juice. The following experiment was 

 tried many times : First, a piece of diatom mat was placed on one side of a 

 calice ; then a bit of Ocypoda flesh was placed on the other. Invariably the 

 Ocypoda meat was seized and swallowed, while the diatoms induced no re- 

 action, except ultimately to be removed from the surface. No kind of purely 

 plant food was taken by any one of the numerous species investigated. 

 However, pieces of plants coated with small animals or soaked in meat juice 

 will be swallowed, and later the vegetal matter ejected. The food of corals 

 consists solely of animal matter. 



This brief summary indicates the mechanisms of corals for catching food, 

 that for keeping their surfaces clean, and the nature of the food of corals. 

 The details of the investigation will be published later. 



Experiments were made on 16 species of Tortugas corals to ascertain the 

 amount of atmospheric exposure they would endure in the shade and in the 

 sun. The details of these experiments will be given in a subsequent pub- 

 lication. Here it will be stated that any of the Tortugas shallow-water spe- 



