APPENDIX. 101 



watcli-glass placed on a card, or board, half of which is 

 black, and the other white; by this means the dark- 

 coloured animalcules wiU easily be recognised on the 

 white surface, and the transparent ones, on the black 

 ground. The minutest kinds often congregate around 

 the margin of the water in the glass. 



Particular species may be selected by means of 

 a glass tube, and placed on a glass slide under the 

 microscope : powers magnifying from 300 to 400 will 

 be required for their proper inspection. The larger 

 and isolated forms, as the Stephanoceros, Limnias, Meli- 

 certa, &c., should be taken up with a feather or camel- 

 hair pencil: by a little practice, an individual may 

 easily be isolated and placed in a live-box, or between 

 two slips of glass. If the animalcules are not at- 

 tached to any vegetable substance, a small fragment 

 of a leaf should be interposed between the two 

 pieces of glass, that they may not be compressed and 

 destroyed. 



Fossil Infusoria, p. 81. — That those infinitesimal forms 

 of existence, whose presence in our lakes, rivers, and 

 seas, can only be made manifest by the aid of the 

 microscope, should be detected in a fossil state, and 

 their aggregated skeletons or shields constitute entire 

 chains of hiUs, and the subsoil of extensive tracts of 



