Pond-Life. 9 



attached to a walking-stick. The principal advantages of this 

 apparatus are its large straining surface (and therefore rapidity 

 of action) and its portability. For the collection of those forms 

 which are attached to water-plants, a small piece of the plant 

 must be placed in a bottle and examined with a pocket-lens in 

 the manner indicated in the early part of this paper. It is never 

 advisable to mix the gathering taken from one pond with that 

 taken from another. Whenever we come across a good form 

 of micro-life it is advisable to take plenty of it, as the minuter 

 forms of life are very uncertain in their habits ; one week a 

 pond may be teeming with some much-valued form, and the 

 next not a specimen may be found. I have many times been 

 disappointed in this very respect, thinking I knew the exact 

 locality of some particular species. Such forms as Melicerta or 

 Carchesium, which may generally be found a second time in the 

 same spot, sometimes disappear in a most unaccomitable 

 manner. Most micro-organisms may be kept for a considerable 

 time in captivity in any sized vessel fi.-om a test-tube to an 

 aquarium holding gallons of water, the great secret of success 

 being to preserve the water at an equable temperature, and not 

 in too strong a light ; for this reason a window having a 

 northerly aspect is the best for aquaria. To maintain life in so 

 small a vessel as a test-tube a hole of the same diameter as the 

 test-tube should be bored through a large cork, the tube pushed 

 through, and the whole floated in a larger body of watel:. 

 Another point to be observed is not to use deep vessels ; as a 

 general rule the depth of the water ought not to be more than 

 half the diameter of the vessel containing it, unless special 

 means of aerating the water be adopted. 



I may here remark that if an object is worth examining under 

 the microscope it is worth being properly illuminated ; in fact it 

 cannot otherwise be satisfactorily examined. I think that our 

 Annual Soiree might be made much more interesting if exhibitors 

 would take a little more trouble in this respect. I am quite 

 aware that it is not very easy to properly exhibit an object in a 

 crowded room, but still a decided improvement might be made 

 in this direction. I have one other suggestion : our visitors are 

 not all microscopists, and the mere name of an object oftentimes 

 carries no meaning with it ; the object is looked upon as a 

 pretty thing and forgotten, but if in addition to the name there 

 was a short description, it would certainly be viewed with more 

 interest. 



I find, as a general rule, that pond-life is best seen on a dark 

 background when using the low or medium powers of the micro- 

 scope ; and this may be done in various ways. Undoubtedly 

 the most satisfactory way of working is to employ a high angle 

 achromatic condenser with both central and marginal rays 



