26 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



placing them upon a slide, examine them with a magnify- 

 ing power of 200 or 300 diameters, noticing : 



a. Great numbers of tri-radiate spicules, formed by 

 three branches of about equal length, which meet at equal 

 angles of 120. 



b. Long unbranched, slender, pointed, needle-like spic- 

 ules. 



c. Occasionally a second kind of tri-radiate spicule, 

 formed by the union of a short branch to the middle of a 

 long branch at right angles. 



d. Make sketches of the spicules. 



e. Wash them thoroughly with water, to remove all 

 traces of the caustic potash, and add to the drop of water 

 which contains them a drop of acetic or sulphuric acid. 

 They soon disappear with active effervescence. 



IV. Imbed half the sponge in paraffine in position for 

 cutting longitudinal sections, and the other half for cutting 

 transverse sections. Tolerably satisfactory sections may 

 be cut from a sponge which, after being placed for about 

 a minute on a piece of blotting-paper to absorb the alco- 

 hol, is allowed to harden in a small quantity of melted 

 paraffine ; but much more satisfactory sections may be 

 obtained in the following manner : Place the sponge in 

 absolute alcohol for about an hour and then lay it on 

 blotting-paper to absorb the alcohol, and then place it in 

 a dish large enough to hold ten or more times its volume. 

 Fill the dish with turpentine, and add all the paraffine the 

 turpentine will dissolve, and keep in a warm room for ten 

 or twelve hours. Then melt some paraffine over a water- 

 bath, and place the sponge in it, and keep it at the melt- 

 ing point for three or four hours. Fold the corners of a 

 piece of writing-paper so as to form a box about an inch 

 long, and half an inch wide and deep. Place the sponge 



