60 MOUNTING AND PREPARATION OF OBJECTS. 



corresponding side of the slip on which the objects 

 lie, the other is allowed to sink gradually to its 

 position, in such a manner, that the fluid goes in a 

 wave from one side to the other, carrying all air 

 bubbles before it. 



Should air bubbles make their appearance, one 

 edge of the cover glass may be raised with a fine 

 needle and an effort made to bring them to the side, 

 as they are inclined to adhere to the edge of the 

 fluid in its passage outwards. They may also be 

 removed by placing the preparation under a small 

 air pump. This latter piece of apparatus will be 

 found very useful for removing air bubbles from 

 structures liable to injury by displacement of the 

 cover glass. 



When Foraminifera are contained in limestone or 

 other hard substances, sections of the substance suffi- 

 ciently thin to be transparent are required, instruc- 

 tions for cutting them will be given farther on. 



We now pass to the preparation of the Diato- 

 maceee, they are closely allied to the Polycystinse 

 and are found in the same deposits. Beautiful forms 

 have been obtained from guano, infusorial earths, 

 sea dredgings, and stomachs of mollusca. They are 

 almost ubiquitous, every road and ditch being filled 

 with them, especially those containing brackish 

 water. They may be obtained from the latter toler- 

 ably free from admixture, if proper care be taken, 

 during then' collection, to leave the bottom mud un- 



