Common Objects for the Microscope. 471 
size, they are of conical shape, flattened above and below, 
and extend right across the bone; the edge which is attached 
presents two distinct pegs which fit into the holes already 
described ; there are three are four of these teeth; the re- 
maining teeth are much smaller and of a more rounded 
shape, resembling little pegs; they are disposed in four 
rows, the lateral rows, articulating with the holes, and the 
central ones with the central groove ; they are very closely 
set. These shoe-bones may be easily separated by placing 
the disc of the animal in a very strong solution of potash ; 
when nicely washed they make an interesting object to 
be viewed by reflected light under a low power of the 
microscope. 
There is a small species of brittle star, called Ophzocoma 
neglecta, a moderate sized specimen will easily lie on a 
shilling, it is very common in rocks between tide marks. 
The skeleton may be easily prepared by immersing the 
creature in a weak solution of potash, and afterwards 
washing it in spirit of wine; it may thus be made beauti- 
fully white. The whole skeleton may be mounted as an 
opaque object ; each of the five plates which surround the 
mouth bears a very close resemblance to a trefoil leaf; the 
structure of the disc is exceedingly beautiful and compli- 
cated ; when nicely prepared it looks under the microscope 
very much as if it were composed of frosted silver, and is 
particularly well adapted to be viewed with the binocular 
arrangement. 
The objects that have been described above, may easily 
be mounted as permanent specimens. After being freed 
by the potash solution from animal matter, they should be 
washed with distilled water in a watch glass, or small por- 
celain basin, they should then be washed again with strong 
spirit, and allowed to dry thoroughly; they may now be 
transferred to a glass slide, upon which a ring of cardboard 
of sufficient depth has been fastened; the cardboard should 
be previously washed in asphalte. The black background 
necessary for throwing up the objects when they are viewed 
by reflected light, may be given by painting a dish of 
photographic black upon the reverse side of the slide. The 
thin glass cover being attached with gum, the whole may 
be finished with a coating of asphalte or other varnish. 
(To be continued. ) 
