IN THE FORMATION OF CORAL REEFS. 345 



SPICULE CONTENT. 



In the determination of the amount of spicules in any colony, the follow- 

 ing procedure was carried out. The colony was removed from the reef 

 without injury to any portion except the expanded base. As in most 

 instances the expanded basal portion of the colony inclosed a mass of cal- 

 careous material which could not be easily separated without the loss of some 

 of the Gorgonian tissues, each colony was cut off close to the base and the 

 base was discarded. The colony was weighed while still wet, cut into small 

 pieces, and the living tissues destroyed by treatment with caustic soda. As 

 a practical working method, it was found most satisfactory to treat the 

 fragments of a colony with a cold 25 per cent solution of the caustic and to 

 remove the pieces of the chitinous axial skeleton rather than to take the 

 time to destroy the latter by prolonged boiling. When the organic material 

 of the ccenenchyma had been destroyed by the caustic solution and sufficient 

 time had been allowed for all of the spicules to settle to the bottom of the jar, 

 the liquid was decanted off and the spicules washed repeatedly in rain-water 

 until no trace of organic debris could be detected in the wash-water. After 

 the last washing, the spicules were collected on a weighed filter, the filter and 

 spicules were dried for 12 hours in a water bath kept at ioo° C. and carefully 

 weighed after cooling in a desiccator to room temperature. 



The reason for making these determinations upon material weighed in 

 a moist condition rather than after drying, which would frequently have been 

 more convenient, was that by the use of the first-mentioned method, the 

 results showed the proportion of spicules to the fresh weight of any colony 

 immediately after it had been collected. This basis of computation made it 

 possible to secure a tolerably accurate estimate of the spicule content of any 

 mass of Gorgonians by simply separating the several species represented and 

 determining the weight of each one. 



In practice, the method worked out satisfactorily except for Gorgonia 

 acerosa. Out of 14 analyses attempted on this form, only 3 could be com- 

 pleted. In all of the other attempts, as soon as the material was subjected 

 to the action of the caustic solution, a thick sirupy mass was formed, in 

 which spicules remained suspended for an indefinite time. Even after the 

 dilution of such a mass with ten times the original volume of water, the 

 spicules were held in suspension, nor could the liquid be forced through a 

 suction filter to separate the spicules. After a few analyses of this form had 

 been attempted, and the results compared, it was found possible to recognize 

 on the reef those individuals which could be successfully disintegrated by the 

 caustic. Presumably this difference in reaction is dependent upon a physi- 

 ological (metabolic) condition of the Gorgonian colony, but of all those 

 studied it was observed in this species alone. 



Previous studies on the ecology of the Gorgonians on the reefs about 

 the Tortugas islands had shown that at least nine-tenths of the bulk of these 

 animals on any reef area are made up of individuals of not more than 12 



