OF MICROSCOPIC OBJECTS. 99 
a lump of fresh chalk into pieces not larger than a walnut; 
_ ‘then crush, but not grind, lest you destroy the forms, into 
a coarse powder that will pass a somewhat wide sieve. Tie 
this, as a pudding, in a stout piece of calico. Drop into 
water and allow the bundle to become saturated, and then 
knead with the hands. This will expel a quantity of milky 
water. From time to time, after allowing the fluid to drain 
off, the cloth should be untied, and retied more closely to 
the mass; and when the contents are reduced to about one- 
third of their original bulk, all large pieces of chalk, portions 
of spines of echini, &c., should be removed, lest they injure 
the more delicate forms. Care must be taken in the 
kneading when the greater portion of the chalk has 
escaped, and at last the bag only shaken until the water 
flows from it almost clear. The whole may then be trans- 
ferred to a bottle of clear water and treated as before 
described. The results, Mr. Robertson says, will be satis- 
factory, and the chalk must be very poor in fossils if 2 Ib. 
would not satisfy any microscopic observer. 
When the Foraminifera are of a larger size, though trans- 
parent enough to be mounted in balsam, the air must be 
first expelled from the interior, otherwise the objects will be 
altogether unsatisfactory. ‘l'o accomplish this they must 
_ be immersed in turpentine and submitted to the action of 
the air-pump. So difficult is it to get rid of this enemy, 
that it is often necessary to employ three or four exhaus- 
tions, leaving them for some time under each. When all 
air has given place to the turpentine, they must be mounted 
in the ordinary way. 
Of all objects which are commonly met with, few are such 
general favourites as the PotycysTINz; and deservedly so. 
Their forms are most beautiful, and often peculiar—stars 
varying in design, others closely resembling crowns ; the 
Astromma Aristotelis like a cross, and many whose shapes 
no words could describe. The greater part, perhaps, of 
those which are usually sold, are from the rocky parts of 
Bermuda; but they are also found in Sicily, some parts of 
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