Anatomy of Gorgonid^. 129 



allowing the acid to evaporate, it was found that beautiful 

 stellate crystals were deposited on the slide. Upon analysis 

 these crystals proved to be those of calcium sulphate. 



In order to avoid any possibility of error on this point, Dr. 

 Andrews kindly made a careful quantitative analysis of the 

 spicules of Plexaiirella dichotoma for calcium sulphate. These 

 spicules were cleaned by boiling in a platinum capsule, in a 

 solution of pure sodium hydrate prepared from metal entirely 

 free from sulphate. The analysis was then made with the 

 following result: 



In 1087 m. g. of the spicules, there was 12.4 m. g. of cal- 

 cium sulphate, or 1.14 per cent. We find then that these 

 spicules are made up of at least three substances — calcium 

 carbonate, calcium sulphate, and silica or some silicate. 



Tests were also made for Jluorine in spicules of Murtcea, 

 but no trace of this substance could be found. 



It is interesting to know that the color of Jliwr spar (fluo- 

 ride of calcium) which is so much like that of these spicules 

 is now known to be organic in its nature, being produced by 

 bitumen.' 



The presence of the siliceous pellicle around the spicule is of 

 peculiar systematic interest. In the sponges, which are now re- 

 garded by many authorities as belongmg to the Ccei.enterata, 

 both siliceous and calcareous spicules exist. In the Gorgoni- 

 D^, which seems properly to be regarded as one of the highest 

 groups of the Ccelenterata, we find that both siliceous and 

 calcareous substances unite in forming each spicule. 



Water-vascular System. The various canals in this 

 species are not so easily grouped as in preceding forms, as 

 they seem to intergrade completel}' in size. 



The Primary canals are not constant in number and differ 

 greatly in size. In cross sections of a branch it is not easy to 



I The purple color of the spicules of many Gorgonias is rapidly dispelled 

 by heat and more slowly by some mounting media such as dammar. It is not 

 superficial but is found thoughout the spicule being evenly distributed like the 

 color of stained glass and no pigment granules can be seen. 



