SEPARATING SPONGE SPICULES. 591 



the preparation, and there is a danger too of the spicules being partly 

 fused by the high burning temperature of the gun cotton. 



The method has the advantage of much saving of time over that of 

 allowing the spicules to settle naturally in a test tube through the process 

 of cleaning and dehydration, and ensures a degree of completeness which 

 is greater perhaps than either this or the centrifuge method. When a 

 very small fragment only of a sponge is available, or where spicules are 

 of very small size or scarce in the specimen, it is especially serviceable 

 as retaining the whole of the spicules within a narrow compass, thus 

 obviating loss of material. Filtration may be accelerated by means of a 

 pressure pump if necessary, though it is better as far as possible to avoid 

 this owing to any additional pressure tending to pack the spicules too 

 closely on the filter or to break them. If through the filter being too 

 hghtly adjusted too rapid filtration should occur, any spicules that may 

 have passed through can of course be recovered by refiltering the waste 

 liquid, and in view of this it is best to observe always the same 

 precaution in regard to cleanness for the flask as for any tubes or pipettes 

 that are used. Any of the latter that have been used in contact with the 

 dissolved gun cotton should be washed in the first instance in ether 

 and alcohol to ensure thorough cleaning and the removal of spicules 

 clinging to traces of the residue. 



Though the method has been employed almost solely for the separa- 

 tion of sponge spicules, there seems no reason why it should not be found 

 of equal service in the treatment of Diatom tests, the shields of Coccoh- 

 thophoridae, or any other minute structures which are uninjured by 

 ether or alcohol. 



