IN THE FORMATION OF CORAL REEFS. 347 



soecies The spicule determinations were consequently restricted to these 

 more abundant forms. In selecting material for the determination, colonies 

 of various sizes were taken, in order to have the final averages cover as wide 

 a series of the different ages of the colonies as was possible without using the 

 larger specimens of any species. The results of the determination on five 

 specimens of the several species are shown in table i . 



As would be expected, those forms having the thickest layer of ccenen- 

 chyma about the horny axis showed the highest percentage of spicules. 

 Those also in which the coenenchyma is most dense, e. g., Eunecia rousseaui, 

 have a much higher spicule content than others in which the coenenchyma 

 is soft-for example, Pseudoplexaura crassa, in which the entodermal canals 

 and the polyps are relatively very large. This last-mentioned difference 

 becomes much more evident when the dry weight of the colonies is taken as 

 the basis for computing the percentage of spicules. In Eunecia rousseaui 

 the proportion between the fresh weight and the dry weight was as too to 85, 

 while in Pseudoplexaura crassa it was as 100 to 55- The same characteristic 

 was especially noticeable in Briareum, in which (although the central axis 

 consists entirely of interlaced spicules) the spicule content was smaller than 

 in several other forms and, indeed, less than the average for the entire 12 

 species on which determinations were made. That the size of the spicules 

 is also an important factor is shown by the fact that while all members of the 

 genus Gorgonia have a relatively thin coenenchyma, the presence of very 

 small, densely packed spicules brings the spicule content well up to that 



shown by other forms. ... u o 



The data contained in table 1 were obtained primarily to give a basis 

 from which the amount of spicules in any mass of Gorgomans could be com- 

 puted without the necessity of making separate determinations on such large 

 Amounts of material as would necessarily be handled in an extended survey 

 of the reefs. In order, however, to have a more reliable check _for these 

 computations, a series of determinations of the spicule content of the Gor- 

 gomans were made from a number of squares, each with sides a yard in 

 length The results of these determinations are shown in table 2. 



In securing the material for these determinations, a square frame made 

 from iron pipe with an area of one square yard, was thrown to the bottom 

 witho t any previous observation of the number of Gorgomans there present. 

 Mr their removal, the colonies were sorted, those of any one species being 

 k pt together, and determination was made of the total amount of spicul s 

 for each kind. For these observations the only selection made was that in 

 pracdcally all instances the specimen was gathered on portions of the reefs 

 where the water was sufficiently shallow to permit one to wade 



Squares 1 to 6 were on the shallow reel west of Loggerhead key and 

 were scattered along a line some 2 miles in length. Square, > 7 to H ^e 

 taken along a line about 0.5 mile in length on the east side of Loggerhead 

 Key Square 15 was on a reef about 3.5 miles east of Loggerhead Key 

 where the Gorgonianfeun^^ 



-^iv three determinationT^rT^ried out on Gor g onia acerosa, for^a^s prev.ously nr.em.oned. 



