ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 929 



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 upon 

 Volvox by even those familiar with the use of the Microscope ; but 

 these may be made so plain that the most inexperienced person may 

 see them without the least trouble, provided that a strong light, with 

 the yellow rays unintercepted, be used, and that sufficient obliquity 

 be obtained by means of a paraboloid or other apparatus, using a 

 compressor with a thin glass top and bottom, and just slightly flatten- 

 ing the largest of the spheres. The 1-2 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 1-inch or even a 2-inch 

 object-glass. 



Then take another of those perplexing objects, the Amcehce, which 

 is regarded as not only hard to find, 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. . . . 

 At first they seem particularly difficult to handle and isolate, being 

 usually found so near the mud, or mixed with it ; but a little study of 

 the habits of these organisms shows a ready way to get over that 

 difficulty. 



Not being swimmers, though doubtless like the Hydra they possess 

 the power to rise or fall in the water, and have besides some slight 

 means of free locomotion, they are usually found to attach themselves 

 to anything with which they may come in contact, generally decayed 

 weeds or mud, and it is only necessary to take advantage of this habit 

 to obtain them quite free from everything else. 



Take up some mud and water in which they are plentiful and fill 

 a thin trough ; lay it nearly or quite flat upon the stage of the Micro- 

 scope and allow it to remain there a few moments ; then quietly empty 

 out the mud and dirty water at one end while you replace it with 

 clean at the other, and the Amoehce will be found attached to the glass 

 as clear as the noonday sun. Care only needs to be taken that the 

 clean water shall replace the dirty without exposing the animals to 

 the air, or they will fall to pieces in countless granules, an experiment 

 worth noting." 



