320 THE FOEAMINIFEEA 



has been turned over upon a fresh area of the cover 

 shp. 



' To avoid importing confusion into the above 

 exposition, I have omitted to refer to certain precau- 

 tions that must be taken. It is obvious that in 

 rubbing down the test in the balsam, especially if 

 the test contain siliceous granules, the hone will 

 itself be worn away, and however slight this wear 

 may be, unless it is corrected, one would in time be 

 making a convex surface, the result of which w^ould 

 be that, when the section is turned over, the greater 

 resistance of the periphery would cause it to be worn 

 away before the central chamber was reached. It 

 is here that the pumice-stone comes into use, and by 

 its continual use during the operation the rubbing 

 surface of the hone is kept quite plane. One small 

 difficulty sometimes attends the use of the pumice- 

 stone. The glassy detritus of the latter adhering to 

 the hone, whilst it assists the operation of rubbing 

 down, has a tendency to get into and clog the 

 section, introducing itself either into the chambers 

 or into any minute air-bubbles that may be present. 

 This glassy mud will soil and confuse the section, 

 but it may be got rid of by means of a strong jet of 

 water from a tap or wash-bottle directed upon the 

 section through a glass tube drawn out to a fine 

 point. When the section is thus cleared, the little 

 spaces left by the process may be filled up with a 

 fine brush dipped in a solution of balsam in chloro- 

 form, after which the section is again w^armed and 

 allowed to cool. If recourse to the tap or wash- 



