CATCHING POLYPS. 49 



by bringing home duckweed, conferva, and other 

 water-phmts from the ponds. Some hauls may be 

 unsuccessful, but if one pond is not propitious others 

 should l>e tried. The plants should be put in a 

 capacious vessel of water, and placed in the light, 

 where, if polyps be present, they will shew themselves 

 Avithin twenty-four hours, either attached to the sides 

 of the glass, or hanging from the plants, or suspended 

 head downwards from the upper film of the water. 

 They are elegant objects, and may be kept without 

 difficulty for some weeks. After being confined in 

 a small quantity of water- for purposes of examina- 

 tion, they should be carefully replaced in the larger 

 vessel, and may thus be used again and again 

 without suffering any injury. A low power, — a three 

 or two-inch glass — or a one-inch, reduced by employ- 

 ing the erector, — is the most convenient for examining 

 the whole creature, but higher powers are necessarv 

 to make out its minute structure. They should 

 be viewed with direct and oblique light, as trans- 

 parent and also as opaque objects. In the latter 

 case the '^Lieberkuhn," or polished silver speculum, 

 is convenient, and if the microscope is not furnished 

 with Lister's dark wells, a small piece of black paper 

 may be stuck behind the object, by simply wetting 

 it with the tongue. 



Although the polyps are remarkable for the sim- 

 plicity of their organization, they do not the less 



