DEPARTMENT OF MARINE BIOLOGY. 159 



THE CORAL REEFS AND THE UFE HISTORY OF CORALS. 



The northern part of the Florida reef from New Cut, opposite Miami, to 

 Pacific Reef, inclusive, both along the outer line of reefs and in the Hawk 

 Channel, was studied. Some dredging was done from off Virginia Key to 

 about a mile north of the jetty at the eastern end of New Cut. Some addi- 

 tional inspection of the reefs and the bottom in the vicinity of the Tortugas 

 was made. The survey of the Tortugas area, however, is not yet complete. 



Mr. George C, Short, U. S. Navy, of Fort Jefferson, according to an 

 agreement, took readings of the temperature of the water at the wharf, in 

 the moat, and at the west flood-gate of the moat at Fort Jefferson, twice a 

 day from June i6, 1911, to June 16, 1912, furnishing a complete and an 

 accurate record for these stations for the period covered. These data, when 

 combined with other available information, will supply accurate information 

 on the temperature of the surface waters of the Florida reef region. 



Water samples for salinity determinations were taken at several stations 

 in the Tortugas, and arrangements were made with Mr. Short to collect 

 additional samples throughout the year in order to ascertain the variation in 

 salinity. 



Although the information on the physical conditions prevailing in the 

 region of the Florida reef is still far from sufficient, additional data are 

 gradually accumulating, justifying the expectation that it will not be a great 

 while before these conditions will be adequately known. 



Besides continuing general observations on the conditions under which the 

 different species of corals live, special attention was devoted to three sub- 

 jects, viz, (i) reactions to food and to non-nutrient particles and the nature 

 of the food of corals; (2) endurance of atmospheric exposure; (3) growth- 

 rate. As it is intended to present a detailed account of the results of the last 

 five years' studies of the Tortugas corals in a forthcoming volume of "Re- 

 searches from the Tortugas Laboratory," the researches of 1912 need be 

 only briefly described in this place. 



The reactions to food and to non-nutrient particles were studied in detail 

 in Mceandra areolata and in more or less detail in 15 other species. Pre- 

 viously the subject had received very little attention. Mceandra areolata was 

 selected as the most suitable species for the preliminary detailed study be- 

 cause of the rather large size of the polyps of the colonies and the ease of 

 obtaining abundant specimens. The mechanisms for capturing food and for 

 ridding its surface of non-nutrient particles were first studied. 



These mechanisms may be briefly described, (i) The entire ectodermal 

 surface is beset with nematocysts, which occur on the tentacles, the oral 

 disk, the column wall, including its downward extension, called the edge- 

 zone, and also on the margins of the mesenterial filaments. The nature of 

 these organs is too well known to require description in these remarks. (2) 

 The entire ectodermal surface is ciliate, the cilia in response to certain stimuli 

 beating toward the oral apertures ; in response to others, beating toward the 

 periphery. (3) The outer surface secretes mucus in which particles may be 

 embedded, the mucus moving under the influence of the beat of the cilia 

 toward the oral apertures or toward the periphery, according to the nature 

 of the response to the stimulation. (4) The tentacles are active and effective 

 in capturing food. (5) The mesenterial filaments, which in many species of 

 corals can be extruded through the column walls, in some instances capture 

 food ; these organs, however, do not seem to play an important role in 

 Mceandra areolata. 



II — YB 



