144 ONYX AND DIPELTIS, 



when they are finally placed together, lay the other cover on. The 

 animal is compressed, and is unable to move. It will be found 

 convenient to have laid the first cover on a minute drop of water 

 on a glass object slide ; by this means it will be held firmly in 

 place on the slide, and the second cover can be laid squarely on ; 

 furthermore, after the second cover is adjusted the slide can be 

 placed on the stage of a microscope and the animal then examined 

 to see if its position is the correct one, and, if not, the fault can be 

 rectified by sliding the upper cover slightly on the lower. 



Supposing the object to be now correctly compressed and 

 arranged, the next step is to fix the covers in place. This is done 

 by moving the two covers to the edge of the slide by means of a 

 needle and touching first one side of the pair and then the other 

 side with the wick of a wax taper or candle which has been just 

 now extinguished. The melted wax from the wick serves to cement 

 the covers together, and they may be afterwards handled with 

 considerable impunity. It will be remembered that directions 

 were given to use less water than would fill the space between the 

 covers ; that was a precaution necessary to bringing both covers 

 into close contact with the hairs that were placed between them, 

 thus securing the requisite amount of compression, and also 

 necessary to securing a firm cementing action of the wax. If there 

 is space between the covers at the edge unfilled by the water, the 

 wax enters it, and if melted wax is then also painted in small 

 quantity on the adjacent outside edge of the covers, a firm union 

 results. 



Allow the covers thus united to lie until all or nearly all the 

 water between them has evaporated. They 

 will then present the appearance illustrated 

 in the adjacent figure. Of course a small 

 amount of water will sometimes remain imme- 

 diately about the compressed animal, and this 

 is often desirable. 

 FlG G^ T E r?em"tS V to: H now the animal could be fixed, stained 

 gether with wax at a a, an( j moun t e d without beino- allowed to change 



and having compressed » » 



between them an object i ts attitude, a result often highly desirable 



