44 PREPARATION AND MOUNTING 



Next to the Diatomacese, no class of microscopic objects has 

 been more looked into of late than the Foraminifera. These 

 animals are almost ail marine, having a jelly-like body enclosed 

 in one or more chambers of shell generally composed of carbonate 

 of lime. The shells are made with minute orifices, through which 

 the pseudopodia (false feet) are extended by which the animal is 

 enabled to lay hold of anything and draw itself along. From the 

 possession of these orifices they derive their name, as foramen 

 means a door or opening. They have been found in every depth 

 of sea hitherto sounded, each depth being abundant in certain 

 species; the lowest beds containing the greatest number of 

 specimens, though with less variation of kinds. In chalk 

 they are found in a fossil state, and may readily be shown (see 

 Chapter III.) ; in limestone and other hard stones they are 

 abundant, and some mountains are composed principally of these 

 shells. 



The methods of obtaining Foraminifera are various. Many may 

 be found upon seaweeds, which should always be examined as 

 soon as possible after gathering. They are found in masses upon 

 some coasts where the waves have carried and left them ; but 

 they are to be found the most abundantly in sand or mud dredged 

 from the bottom of the sea. They must, however, be cleansed and 

 separated from the mass of impurity with which they are usually 

 mixed. This may be done in various ways, according to the 

 nature of the accompanying matter. If sand alone, as is frequent- 

 ly the case, the whole mass must be thoroughly dried, and then 

 stirred up in clean water. The* sand will soon subside by its own 

 weight, but the chambers of the Foraminifera, being filled with 

 air, will float upon the surface, and may be skimmed off. There 

 is, however, one objection to this mode of proceeding some of 

 these objects are so minute, the chambers containing compara- 

 tively so small a quantity of air, that they sink and are cast away 

 with the refuse sand. On this account it is preferable to take the 

 trouble of searching certain soundings under the microscope, using 

 the camel-hair pencil, or some other contrivance before mentioned, 

 to extract those objects which are required. To clean the Fora- 

 minifera, Professor Williamson advises to transfer the specimens 

 to an evaporating dish containing a weak solution of caustic potash. 



