MICROSCOPES FOB INFrSOEIA. 99 



strained. At first, nothing appears on the linen except a mere stain, 

 but, by repeating the operation, a considerable quantity will be 

 obtained. If not very gelatinous, the Avater passes fi-ecly through 

 the linen, from which the specimens can be scraped with a knife ; if 

 otlierwise, the water must be poiu'ed dii-ectly into tht^ collecting 

 bottle, as force would destroy them. Some species of Staurastrum, 

 Pediastrum, &c., form a greenish dii-tj^ cloud upon the stems and 

 leaves of aquatic plants — to collect these, requii'e much care ; the 

 slightest touch will often break up and disperse them. To secui'e 

 them, let the hand be passed into the water and beneath the cloud, 

 the palm upwards and the fingers apart, so that the leaves or stems of 

 the invested plant may lie between them, and as near the palm as 

 possible ; then close the fingers, and keeping the hand in the same 

 position, but concave, di'aw it cautiously towai'ds the sui-face, when, 

 if the plant has been allowed to slip easily, and with an equable 

 movement thi'ough the fingers, the BesmidiecB, in this way, bi-ush 

 off, and will be found hdng in the palm. The greatest difficult)^ is 

 in withdra^-ing the hand from the surface of the water, and, probably, 

 but little will be retained at fii'st ; practice, however, will soon render 

 the operation easy and su.ccessful. 



The reproductive bodies, or Sporangia of Besmidiece, are collected 

 more frequently by the last than the preceding methods. When your 

 bottles are carried home, they will, apparently, contain only foul water, 

 but, if it remain undistiu'bed for a few hours, the Desmidiece will sink 

 to the bottom, and most of the water may then be poui-ed off. If a 

 little fresh water be added occasionally to replace that which has been 

 drawn off, and the bottle be exposed to the light of the sun, the 

 Desmidiece will remain unaltered for a long time. Mr. Ralfs mentions 

 he has, in this way, kept specimens of Euastrum insigne in good 

 order for five months. (Abridged from Mr. Kalfs' introduction to 

 British Desmidiea?, p. 37.) 



Special instructions where necessary for collecting certain families 

 of Infusoria, -will be found in the general remarks prefixed to them 

 in Part III. 



Section II. — On Microscopes for Examinining Infusoria. — A good 

 microscope cannot be fully appreciated imtil it is brought to the 

 examination of HAing Infusoria. It is true, that we may make use 



