330 NATURAL HISTORY OF OUR SHORES 



until ebullition begins ; then stand the test tube in a cup 

 or small jar, with a saucer underneath ; there will be 

 violent action, and the nitric acid will boil over the top 

 of the tube (that it why it must be stood in cup and saucer). 



The bit of sponge may run to the top of the tube with 

 the froth ; push it down with a glass rod. As soon as the 

 sponge is dissolved fill up with clean water (save what has 

 overflowed, and put all into the tube), and allow the spicules 

 to settle. Wash thus two or three times. If any little bits 

 of sponge, now of a yellow colour remain, boil once more in 

 nitric acid, and wash. 



There will be a surprising mass of the beautiful spicules, 

 as a snow-white deposit, at the bottom of the tube. Some 

 should be mounted dry, on black background, others in 

 balsam. These present no difficulty. 



To prepare the Odontophores of Mollusca. The Gastropod 

 molluscs, the Cephalopoda, Scaphopoda, and the Pteropoda 

 all possess a toothed ribbon, which is variously described 

 as the " Odontophore" " Radula" " Lingual Ribbon" and 

 " Palate" This is a narrow, chitinous strip of membrane, 

 closely set with fine-pointed, flinty teeth in regular pattern. 



These Odontophores are not only interesting objects of 

 study, but they are among the most beautiful objects upon 

 which the microscope has ever been brought to bear. Their 

 use has been alluded to in writing of the molluscs which bore 

 holes through the shells of the oyster, limpet, etc. The 

 non-boring molluscs employ them as rasps for mowing 

 down fine vegetation, and for breaking up food generally. 



These are easily prepared for the microscope, no skill in 

 dissection being necessary. All that need be done is to 

 cut off the anterior part of the mollusc, and place this in 

 its entirety in a bottle, with a fairly strong solution of 

 caustic potash. (An ordinary stick of this, as sold at the 

 druggist's, to about half-a-pint of water.) In a short time 

 the mass will swell up, gelatinise, and finally dissolve, leav- 



