CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. 53 



"3. Ufider artificial conditions. — As corals can be grown In aquaria, numerous 

 experiments on both gametic and vegetative variation are possible. The behavior 

 with reference to at least seven factors can be studied: Food supply, heat, light, 

 character of bottom, strength of current, degree of salinity of the water, various 

 kmds of impurities in the water. Even the influence of pressure might be studied. 



"The study of variation in nature should go more or less in hand with the 

 experimental work. It is to be hoped that studies of the kind here outlined will 

 be undertaken by some of our marine biological stations, and that other stations 

 that can undertake such work will be established, for until these studies are made 

 it will not be possible to understand variation in the Madreporaria. Until variation 

 is understood the systematic work must be more or less unreliable; and until more 

 is known concerning the physiology of corals we can not understand the factors 

 that determine their distribution." 



In my Hawaiian paper I devoted special attention to the relations of 

 corals to depth, temperature, and character of bottom, and under the caption 

 "Additional factors governing the distribution of Madreporaria," it is said: 



"Dana says:^ 'The range of temperature 85° to 74° gives sufficient heat for 

 the development of the greater part of coral-reef species; and yet the temperature 

 at the 100-foot plane in the middle Pacific is mostly above 74°. The chief cause 

 of limitation in depth is the diminished light, as pointed out by Professor T. Fuchs.' 



" Pressure and diminished light are both correlative with depth. Both factors 

 need further investigation. Another factor that needs study is the food supply, 

 and probably the oxygen content of the water. Some of the factors to which con- 

 siderable attention has been paid are not considered here, such as position with 

 reference to the lines of the breakers, relations to the fall and rise of the tides, etc. 



"As yet comparatively few facts bearing upon the fundamental principles which 

 determine the distribution of corals have been collected. Most authors have 

 contented themselves with merely mentioning the station and depth at which a 

 given form was procured; they usually have not utilized even these data in attempts 

 to discover any underlying principles. We need much more information and more 

 tabulations of the physical surroundings under which the forms, from individuals 

 to genera, have Hved; and a wide range of phenomena should be made the subject 

 of experimental physiological investigation. 



"The understanding of the relations of organisms to their physical environment 

 is of the utmost importance to the paleontologist, for it is by the application of 

 such knowledge that he is able to reconstruct the conditions under which organisms 

 now extinct once lived." 



In the vi'ork on the corals in Florida and the Bahamas, their relations 

 to the following factors have been specially studied : Depth; currents, winds, 

 breakers; character of bottom; sediment; mechanisms for catching food; 

 nature of the food; light; temperature; salinity; atmospheric exposure; con- 

 ditions favorable and unfavorable for the settling of planulae; duration of 

 the free-swimming larval stage; organic associations unfavorable to their 

 life; normal organic associations; growth-rate. The results of all these 

 investigations have been published in progress reports in Year Books Nos. 7 to 

 14 of the Institution, and in other short papers, but they have not appeared, 

 except in abstract, under a single cover. References to the series of articles 



'U. S. Nat. Mus. Bull. 59, pp. 46-47, 1907. 



