The brilliant scientist refers to euglena ("yoo-GLEEN-ah) as "animals" and the encyclopedia says they are photosynthetic, unicellular, aquatic, motile, freshwater organisms, "characterized by the presence of chlorophyll, a reddish eyespot, and a single anterior flagellum...They resemble plants in that they have chloroplasts, but they also have gullets and lack cell walls, like animals." Do we now know whether they are plants or animals?

Place a culture of euglena in a long test tube sealed with a cork or rubber stopper. Hold the test tube in a horizontal position. Using a hand lens, you will see that the animals become evenly distributed in a short time.

Now hang a piece of dark cloth over half the test tube. Do this gently so as not to disturb the animals. After an hour, remove the cloth and immediately observe again.

You will find that the euglena tend to be in the lighted portion of the tube; the animals sense light and seem to have a preference for it.

You can test the influence of light on one-celled plants by placing cultures of them in locations with different lighting conditions.

What is the basic difference between animal and plant? Is it the presence of a brain? Well, we all know a few people who seem to lack that...