186 CARNEGIE INSTITUTION OF WASHINGTON. 



small pieces of this coral does not revive the growth-rate, such separated 

 pieces growing at the characteristic rate of the major stock from which 

 they were removed. 



"WTiile some species of Florida corals, such as Orbicella annularis, 

 may continue to grow for at least 300 years, most of the reef species, 

 such as Acropora, attain full size in 10 years or less, and then cease to 

 grow, but still survive for an undetermined period until overcome by 

 the attacks of seaweed, bryozoa, millepora, boring algse, other organ- 

 isms, or silt, the encroachments of which, due to physiological senes- 

 cence, the coral has become unable to resist. These factors are the 

 common causes of death of coral-heads on the reefs. 



The impossibility of forming any definite plan for the year's work 

 until the termination of hostilities, and especially the unprecedentedly 

 high cost of essential materials and of labor, and the continued absence 

 of many of our leading investigators in war work, have made it difficult 

 to carry out our normal program of research. 



The long-delayed and very expensive repairs to the yacht, launches, 

 and laboratory buildings have also consumed so much of our annual 

 appropriation that we have been obliged to curtail much research 

 we had hoped to carry out during the year. Prices of apparatus and 

 of most essentials were quite double those prevailing in 1917 and de- 

 livery of all manufactured articles was delayed to such a degree that 

 in some cases our research w^ork suffered seriously. 



The following investigators studied during the year under the aus- 

 pices of the department: 



Dr. Paul Bartsch, January 1 to 23, May 1 to 17. Heredity of characters in Bahama- 

 Florida cerions. 



Dr. Joseph A. Cushman, May 14 to June 3, at Tortugas. Foraminifera. 



Professor R. A. Daly, May 14 to June 3, at Tortugas; July 21 to September 16 in 

 Samoa. Geology of Tutuila and other islands of Samoa. 



Professor Ulric Dahlgren. Development of electric muscles in the electric eel, Gymnotus. 



Dr. Richard M. Field, June 5 to 19, Tortugas. Limestones of Florida reefs. 



Professor W. H. Longley, June 5 to July 1, Tortugas. Submarine study of ecology of reef 

 fishes. 



Professor J. F. McClendon, June 5 to 19, Tortugas. Anesthesia in marine animals. 



Alfred G. Mayor, Tortugas, and Tutuila, Samoa. Effect of diminution of oxygen on rate 

 of nerve conduction. Rate of nerve conduction in regenerating tissue lacking 

 muscles. Growth-rate of Samoan corals at various depths down to 8.5 fathoms. 

 Effects of currents in transporting sediment over reefs. Losses in reef material 

 due to boring alga?, solution, holothurians, etc. Detection of ocean currents 

 by observing their hydrogen-ion concentration. 



Professor Asa A. Schaeffer, May 17 to June 19. Marine amcebas from Tortugas. 



R. C. Wells, June 7 to 19. Carbon-dioxid content of Tortugas sea-water. 



A fund was deposited with Dr. C. William Beebe to obtain information 

 respecting the breeding-season of Gymnotus, the electric eel of Guiana, 

 in order to enable Professor Ulric Dahlgren to make plans for the study 

 of its embryology and the development of its electric organs. 



