CYTOLOGY 25 



trail of mucus which they give out in a continuous stream when in 

 motion. 



A high magnification usually shows fine transverse lines across 

 the diatom shell. These lines are so fine in some species of diatom 

 that these little plants serve as test objects to test the optical powers 

 of a microscope. 



Oscillaria. The oscillaria is a thread-like motile alga, provided 

 with a bluish-green chlorophyll. The threads are not long and the 

 motion consists in a jerky, oscillatory movement of the ends of the 

 threads. 



Swarm spores of the fresh-water algae are unicellular and are the 

 best examples of motile plants of the lower order. The first thought 

 that comes to one while watching the active little plants is, Why 

 do they move? The animal lives upon plants or other animals and 

 must be provided with some means of catching its food. The green 

 plant lives upon carbon-dioxide gas and water, with the salts dis- 

 solved in the water. But as the swarm spores live in water in which 

 CO 2 and mineral salts are dissolved, why should they be endowed 

 with locomotion? 



Laboratory Exercises. 



1. Appliances. Microscope with high and low power; slides, plain 

 and celled; cover-glasses; pipette. 



2. Preparation. Several well-stocked aquaria, stocked with pond 

 scum, slime, ooze, and pond water gotten from stagnant ponds which 

 lie in not too close proximity to a manufacturing district or railway. 

 By stocking aquaria from different ponds one is likely to find all 

 the above-named forms (except protococcus) and perhaps many 

 other forms. Keep the aquaria near the windows, where they will 

 get the warm sunshine during the day. In addition to the above, 

 one will do well to prepare an infusion of hay and keep the same 

 in a 500 c.c. beaker. The amceba, paramrecium, and dileptus are 

 likely to appear in the liquid after a few days, while it will swarm 

 with myriads of bacteria. 



3. Observations. (1) Take a drop of water from near the top or 

 bottom of one of the aquaria, place it upon a slide, put a clean 

 cover-glass gently over it, and focus under the low power of the 

 microscope. Look for any of the organisms above described. As 

 the aquaria will probably differ somewhat the one from the other 

 in the organisms which they contain, the student will do well to 

 examine the contents of all the aquaria. Study all forms of life. 

 Determine, if possible, in the first place whether an organism is 

 plant or animal. If it seems to be plant, determine whether or not 

 it represents one of the common algse above described. If so, make 

 a careful study of it. 



