DISC HOLDER ROTIFER-TRAP. 83 



manently mounted. The object is attached to the disc by 

 the aid of gum, or any other suitable adhesive material, 

 and when placed in the holder for observation, the disc can 

 be rotated in both 

 vertical and horizon- 

 tal directions. These 

 discs are very useful 

 for many objects, 

 especially those not 

 needing a cover, and 



Messrs. Beck supply 



^ * FIG. 69. 



boxes into which they 



are fitted when not in use, so that they may be kept excluded 

 from the dust. 



With many objects, in order to examine them minutely, 

 all that is necessary is to place them upon a glass slip, 

 add a drop of the right medium, and cover with a thin 

 covering glass. 



This method of working is all very well for organisms 

 which are still, or comparatively so ; but when we come to 

 examine Rotifers, the Entomostraca, and other active forms 

 of life, we find means are required to keep them in one 

 position. Suppose, for instance, we wish to examine an 

 Entomostracon, which turns out to be Bosmina longirostris : 

 during its rapid motions through the water we would be 

 apt to come to false conclusions concerning it, but if we 

 prevent the organism from moving it can then be studied in 

 all its details. 



The simplest and least expensive way of examining the 

 Infusoria and other moving micro-organisms is by the use 

 of the Rotifer-trap of Mr. F. Bedwell. This consists of a 

 few filaments of cotton wool placed upon the under glass of 

 a " live-box." The organism contained in a drop of water 

 is then run over it, and eventually becoming entangled 



G 2 



