no evolution: the ages and tomorrow 



formed, but an animal with such pigment is well aware of 

 fine gradations in the intensity of light. Stentor, a very 

 beautiful trumpet-shaped animalcule, has one of these 

 highly irritable spots near its anterior end. Stentor prefers 

 a shadowy habitat; if it swims into the line of light, it im- 

 mediately backs away and turns, then goes forward again. 

 If there is a beam of light through the shadowy water, Sten- 

 tor will avoid it by the following reaction: the animal 

 arrives at the edge of the light and turns as it reacts to its 

 receptor; it heads off in another direction and again reacts if 

 it comes into the beam, thus constantly remaining in the 

 shade. When it is in a large patch of light, it will swim 

 straight only when its sensitized spot at the front end lies 

 in the shadow of the body, and by this reaction it will 

 eventually arrive in shaded waters. Euglena, which has the 

 capacity to manufacture its own food in the presence of 

 light, has a pigment spot which sets up a reaction the reverse 

 of Stentor— the animal moves into and stays in the light. In 

 some of the many-celled animals, the earthworm, for in- 

 stance, cells sensitive to light are scattered all over the body 

 in the epidermis; they "feel" the light, there is no "sight" 

 involved. 



Soon in the rising series of animals the scattered sight- 

 cells are brought together to form the first primitive eye, the 

 cells being gathered into patches with nerves from each cell 

 leading into the brain. The image formation is at first very 

 crude, but nature's great powers of organization add im- 

 provement after improvement in the kind and arrangement 

 of the cells and in the complexity of the brain centers which 

 receive the light stimulus. At first the eye can distinguish 

 only vaguely the outline of moving objects and patches of 

 light and shade. Here is obviously a great tool for the use 

 and enjoyment of understanding, and, after preliminary 

 trial, nature organizes an eye of multiple facets, the multiple 

 images of which the brain turns into one spatial image. Some 

 of the more advanced of these eyes, like that in the bee, are 



