128 Natural History Bulletin. 



the periphery to the center, growing smaller and smaller, until 

 the last vestige disappears with the last bubble cf gas, and we 

 see simply the shadowy outlines of the perfectly transparent 

 pellicle, which retains every detail of the original form of the 

 spicule, but will shortly collapse and be nothing but a filmy 

 fracrment of silica of extreme tenuity. 



This pellicle withstands both boiling in potash and treat- 

 ment with strong hydrochloric acid. Its chemical properties 

 and appearances under the polariscope show that it is com- 

 posed either of silica or of some silicate. Dr. Andrews re- 

 gards it as more likely to be the former. 



It is hard to conceive of the entreme tenuity of the pellicle. 

 It is with difficulty that its outlines can be made out with the 

 microscope and its actual weight is so little that the combined 

 weight of all the pellicles investing 1087 m. g. of spicules was 

 not capable of affecting the balances of the scales used in 

 analysis. 



2d. The amount of organic matter in the interior of the 

 spicules is not appreciable. This is in accord with the opinion 

 of Kolliker and opposed to that of Pouchet and Myevre. 



Thinking that the spicules cleared by boiling in caustic 

 potash might be unsatisfactor}- in attempting a solution of this 

 point, I carefully dissected some spicules out of an alcoholic 

 specimen of Eunicea tourncforti and then treated them with 

 acid as described above. They were attacked by the acid at 

 definite points, the whole interior was disintegrated and 

 completely disappeared leaving nothing but the pellicle, 

 as was the case with spicules which had been cleaned in 

 potash. Not a trace of any residue could be seen under the 

 microscope inside the siliceous pellicle spoken of. 



3d. Calcium carbonate constitutes nearl}' all of the interior 

 of the spicule. Rough tests show that at least 98 per cent, of 

 the entire spicule is composed of this substance. 



4th. Next to calcium carbonate, calcium sulphate enters 

 most largely into the constitution of the spicules. 



After treating the spicules with acid, as above described, and 



