MICROSCOPIC PREPARATIONS IN MARINE ZOOLOGY 329 



with mixed gatherings. The photo-micrograph (Fig. 2), is 

 made from such a slide. 



To obtain good results lightly gum the glass slip and 

 let it dry, put on a pinch of shells, breathe upon them, 

 then tip of? the loose ones and remove any bits of foreign 

 matter or bits of broken shells. Place slip and all in a 

 wide-mouthed bottle, in benzoline, and leave them for 

 some days, giving a little shake occasionally, until all the 

 air in the shells is expelled ; then lift out the slide, put on 

 a drop of balsam and benzole, cover, and clip. Finish in 

 the ordinary way. 



A more rapid but less certain way is to put the balsam 

 and benzole on the shells without a preliminary soaking ; 

 put on cover and clip, and then hold the slide (cover up- 

 wards) over the flame of the spirit lamp until the balsam 

 boils. There will be a great commotion of bubbles beneath 

 the cover as the air rushes out from the shells and the 

 balsam fills them, but as a rule all bubbles disappear, and 

 the slide is ready to clean and finish. 



Preparing Spicules of Sponges. To obtain the spicules 

 free from organic matter for mounting, either dry or in 

 balsam, the soft parts are destroyed by boiling the sponge 

 in caustic potash or, if a Siliceous sponge, in nitric acid. 



If it is Calcareous spiculed place it in a test tube with 

 water and a bit of caustic potash (about the size of a French 

 bean) ; boil over the spirit lamp until no lumps of sponge 

 remain ; let the deposit settle ; pour off the liquid, and fill 

 with clean water. Repeat this wash two or three times, and 

 the spicules will remain at the bottom, quite clean. They 

 can then be placed in a tube until wanted, either in water 

 or in dilute spirit. 



The Silicispongia are best managed by means of nitric 

 acid. This requires a little care. Place the piece of 

 sponge in the test tube, and just rather more than cover 

 it with strong nitric acid. Warm it over the spirit lamp 



