XX PRESIDENT S ADDUESS. 



get tlio Volvox at tlie bottoiii of the earthenware vessel as 

 tliickly together as I Hke. They may then be picked ^^p by 

 means of the syringe and placed in any quantity or density 

 upon a slide or compressor, care being taken in showing them 

 to allow only just sufficient depth between the top and bottom 

 glasses to allow them to revolve freely through the water. The 

 same result I have obtained by taking advantage of the effects 

 of heat and cold upon these organisms. If they are freely 

 distributed about the water in which they are stored it is only 

 necessary to take some ice and lower the temperature of the 

 water to bring most of them to the bottom, or if they are at 

 the bottom, mixed with dirt as they often are, then to place the 

 jar near the fire, and so stimulate them, and bring all that are 

 living and fresh to the top, when they may be brought to one 

 side of the vessel by directing upon it a bright light. 



It is usually regarded as a difficult matter to see the cilia 

 Tipon Volvox by even those familiar with the use of the micro- 

 scope ; but these may be made so plain that the most inex- 

 perienced person may see them without the least trouble, provided 

 that a strong light with the j/ellow rays unintercepted be used, 

 and that sufficient obliquity be obtained by means of a para, 

 boloid or other apparatus, using a compressor with a thin glass 

 top and bottom, and just slightly flattening the largest of the 

 spheres. The half-inch is best ; but when they are once seen 

 and all things are properly arranged, there is no real difficulty 

 in watching their flashings with a one-inch or even a two-inch 

 object-glass. 



Then take another of those perplexing objects, the Amoeba, 

 which is regarded as not only hard to lind, but harder still to 

 see, and let me say that the two difficulties resolve themselves 

 into the latter one only, there being no trouble whatever in 

 obtaining specimens. 



As I have already said, 1 usually look for these either 

 without any optical assistance at all or with nothing more than 

 an ordinary pocket-lens, and that is generally quite sufficient. 

 But of course it needs to be ponited out that these organisms 



