OF MICROSCOPIC OBJECTS. 67 



these, however, though they lose some beauty by the ordinary 

 mode of drying, will by steeping for some time in turpentine not 

 only be freed from the air-bubbles, but suffer so little contraction 

 that they are a worthy addition to the cabinet. 



Another class of objects is the spicula met with in sponges, &c. 

 These are often glass-like in appearance and of various shapes ; 

 many are found resembling needles (whence their name) ; some 

 from the synapta are anchor-like, whilst others are star-like and 

 of complex and almost indescribable combinations. As some of 

 these are composed of silex and are consequently not injured by 

 the use of nitric acid, the animal substance may be got rid of by 

 boiling them in it. Those, however, which are calcareous must 

 be treated with a strong solution of potash instead ; but which- 

 ever way is used, of course they must afterwards be freed from 

 every trace of residue by careful washing. 



These spicules may be often found amongst the sand which 

 generally accumulates at the bottom of the jars in which sponges 

 are kept by those who deal in them, and must be picked out with 

 a camel-hair pencil. The specimens obtained by this means will 

 seldom if ever require any cleaning process, as they are quite free 

 from animal matter, &c. 



In the former chapter was noticed those insects or parts of 

 them which are usually mounted dry. When they are large and 

 too opaque to admit of the dry treatment, they must be preserved 

 in Canada balsam or fluid. The first of these may now be con- 

 sidered. 



It may be here mentioned, that with these objects much heat 

 must not be employed, as it would in some instances give rise to 

 a cloudiness, and almost invariably injure them. 



In killing the insect it is necessary not to rub or break any part 

 of it. This may be performed by placing it in a small box half 

 filled with fragments of fresh laurel leaves, by immersion in tur- 

 pentine or strong spirit, as also in solutions of various poisonous 

 salts. After which it may be preserved for some time in turpen- 

 tine or other preservative liquid (Chapter IV.) until required. 

 As an assistance to the student, I believe that I can do no better 

 that give him the plan pursued by my friend Mr. Hepworth, 

 whose specimens arc in every way satisfactory ; but when his me- 



