74 THE BIOLOGY OF THE ANIMAL 



however, on account of the simplicity of its structure. 

 The following study is based upon alcoholic material, 

 which the student may prepare for himself or may ob- 

 tain from sources mentioned in the introduction. Speci- 

 mens of two kinds may be prepared, the first to retain 

 the spicules, the second to be decalcified so that the tis- 

 sues may be examined. The first kind of specimens may 

 be dried, or may, while stiU living, be placed into seven- 

 ty-five per cent, alcohol, where they should remain for a 

 day, then they may be transferred to ninety per cent, 

 alcohol and left until needed for examination. In each 

 case the bulk of the alcohol should be several times that 

 of the specimens. Decalcified specimens may be pre- 

 pared by placing either living or alcoholic sponges into 

 one per cent, to two per cent, solution of chromic acid 

 for twenty-four to thirty-six hours, during which time 

 the acid removes the spicules by dissolving them, but 

 hardens and preserves the cellular tissues. The decalci- 

 fied sponges are then to be passed through the various 

 grades of alcohol, being left in the strongest until it is 

 no longer discolored by the acid, embedded in ceUoidin 

 or paraffine, and sectioned free-hand with the razor or, 

 better, on the microtome. 



Other material required : Delafield's heematoxylin, 

 borax carmine, or acetic acid carmine, fifty per cent, 

 glycerine or Canada balsam, watch-glass, test-tube, alco- 

 hol lamp, pipette, potash, compound microscope, and hy- 

 drochloric acid. 



Method of Examination. — Study first, with or with- 

 out the hand-lens, the entire specimen in the living state 

 if obtainable ; if not, alcoholic material may be used, 

 the specimen being kept in a watch-glass or small dish 

 containing fifty per cent, alcohol. Other specimens. 



