102 PKEPARATION AND MOUNTING 



if, however, they have been dried, they should be soaked in 

 cold water for a day or two before being submitted to the 

 following processes : 



1. After selecting perfect specimens of suitable size, im- 

 merse them in water heated to about 120, and place them 

 under the receiver of an air-pump. Slowly exhaust the 

 air, when bubbles will rise and the water appear to be in a 

 state of active ebullition. After a few minutes re-admit the 

 air and again exhaust, repeating the process three or four 

 times. This will displace the air from most, if not all, of 

 the class. 



2. Remove the specimens and allow them to drain upon 

 blotting-paper for a few seconds ; then place them in an 

 earthen vessel fitted with a cover, and previously heated to 

 about 200. This heat may be easily got by placing the 

 vessel for a short time in boiling water, wiping it imme- 

 diately before using, with a thick cloth. The specimens are 

 then dropped into this, covered with the lid, and imme- 

 diately placed under the receiver of the air-pump, and 

 the air rapidly exhausted. By this means they are dried 

 completely, and so quickly that the cells have no time to 

 wrinkle. 



3. In an hour or two remove them from the air-pump 

 and drop them into a vessel of perfectly transparent cam- 

 phine. This may be quite cold when the horny, tubular 

 polypidoms, as those of the Sertulariae, are used ; but should 

 be previously heated to lOO^ 3 when the calcareous, cellular 

 Polyzoa are the objects to be preserved. The vessel should 

 be covered with a watch-glass and placed under the re- 

 ceiver, the air being exhausted and re-admitted two or three 

 times. 



4. The slide which is to receive the specimen should be 

 well cleaned and warmed so as to allow the balsam to flow 

 freely over it. This must be applied in good quantity, and 

 air-bubbles removed with the needle-point. Take the poly- 

 pidom from the camphine, drain it a little, and with the 

 forceps immerse it fully in the balsam. The glass to be 



