66 PREPARATION AND MOUNTING 



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 immediately before use with a thick cloth. 

 The specimens are then dropped into this, covered with the lid, 

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

 the air rapidly exhausted. By this means they are dried complete- 

 ly, 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 camphene. This may 

 be quite cold when the horny, tubular polypidoms, as those of the 

 Sertularise, are used; but should be previously heated to 100 

 when the calcareous, cellular Polyzoa are the objects to be pre- 

 served. The vessel should be covered with a watch-glass and 

 placed under the receiver, 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 re- 

 moved with the needle-point. Take the polypidom from the 

 camphene, drain it a little, and with the forceps immerse it fully 

 in the balsam. The glass to be laid upon it should be warmed 

 and its surface covered with a thin layer of balsam, and then low- 

 ered gradually upon it, when no bubbles should be imprisoned. 

 A narrow piece of card-board at each end of the object for the 

 cover to rest upon, prevents any danger of crushing the specimen. 



This mode of mounting polypidoms, &c., seems to give almost 

 the complete beauty of the fresh specimens. They are very beau- 

 tiful objects when viewed with common light, but much more so 

 when the polarizer is used (in the manner described a little far- 

 ther on). 



To the above instructions there can be little to add ; but I may 

 here mention that some young students may not be possessed of 

 the air-pump, and on this account put aside all search for those 

 specimens which need little looking for at the seaside. Many of 



