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. To 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 POLYCYSTIN.S; ; 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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