THE SPONGES (PORIFERA) 305 



Provide a half dozen or more short test tubes with a stand made 

 by boring holes of suitable diameter in a piece of inch board. 

 First make sure that you have in hand parts of the same sponge 

 only. Place in the first tube a dozen or more clean gemmules, 

 some of them cut in half with a sharp knife, and about an equal 

 bulk from the remainder of the sponge; cover with a few drops of 

 strong nitric acid that has been previously brought to a boil in 

 another tube and set aside, the purpose being to corrode away the 

 crust but not the chitin of the gemmules. In a few minutes, when 

 most of the gemmules incline to settle at the bottom, pour off the 

 acid into the next tube, wash carefully with several lots of pure water, 

 replace it with alcohol and set the tube aside to settle. Put into 

 the acid in the second tube a small quantity of all parts of the 

 sponge, adding more acid if necessary, and boil carefully over a 

 spirit lamp to thorough disintegration. When that is effected fill 

 this tube also with water and set it aside to settle. The smaller 

 spicules settle very slowly. It may be well to shake the tube a little 

 in order to separate the darker particles from the pure white. When 

 the mass has settled, carefully pour off the water with the impuri- 

 ties, wash the residue with fresh water and let it stand, after which 

 a mount may be made from this tube. Spread the spicules evenly 

 and not too thickly on a slide, and let them dry thoroughly before 

 adding balsam and a cover glass. This amount will of course fur- 

 nish an epitome of the sponge but will not show the exact relations 

 of the minor spicules to the gemmules. This can only be seen after 

 two or more applications of alcohol to the first tube have removed 

 the acid mixture ; to keep out the air, cover with benzol until fully 

 ready for the balsam. Distribute a few of the gemmules, with some 

 spicules, upon a second slide and mount in balsam before the air 

 penetrates them. A fragment of the dry filmy dermis mounted in 

 balsam will determine the presence or absence of dermal spicules 

 and fix positively the standing of the sponge according to the key. 



If all the smaller spicules distinguished by this process are acer- 

 ates, that is, more or less cylindrical, whether straight or curved, 

 smooth or spined, pointed or abruptly terminated, the specimen 

 under examination may unhesitatingly be placed in the genus Spon- 

 gilla. All others, unless entirely novel, will show some modification 



