142 BEHAVIOR OF THE LOWER ORGANISMS 



to exist in Stentor and Euglena ; indeed, the evidence seems clear that 

 these reactions take place in essentially the same way throughout the 

 group. In Cryptomonas ovata, and less completely in the swarm 

 spores of Chlamydomonas and Cutleria, the present writer has observed 

 that the reaction to light is of the same character as in Euglena. We 

 shall pass in review certain general features of the reaction in other 

 infusoria, as described by various authors. 



As we have before noted, most colorless infusoria give no indication 

 of sensitiveness to light. But color is not absolutely necessary in order 

 that reaction to light may occur, as is shown by the fact that Amoeba 

 reacts to light. Even in the infusoria, colorless species may react to 

 light when such behavior is distinctly beneficial to the organism. A 

 species of Chytridium, a colorless flagellate that is parasitic on the 

 green organism Haematococcus, reacts to light in the same manner as 

 Haematococcus, collecting as a rule in lighted regions, or at the side of 

 the vessel next the source of light (Strasburger, 1878). This, of course, 

 aids it in finding its prey, which collects in the same regions. Several 

 other colorless infusoria that are parasitic on green flagellates have 

 been found to react to light in the same manner as their prey. Ver- 

 worn (1889, Nachschrift) found that the colorless ciliate Pleuronema 

 chrysalis reacts to a sudden increase in the intensity of light by a rapid 

 leaping movement, — evidently a strongly marked avoiding reaction. 

 Certain colorless infusoria react, as we shall see later, to ultra-violet 

 light. 



In the green ciliate Paramecium bursaria the reaction to light de- 

 pends, according to Engelmann (1882), on the amount of oxygen in 

 the water. This animal contains chlorophyll, which produces oxygen 

 in the light. When there is little oxygen in the water, the organism 

 gathers in lighted regions, thus of course increasing its store of oxygen. 

 When the individuals in the light come to the boundary of a dark region, 

 "they turn around at once into the light, as if the darkness was unpleas- 

 ant to them" {I.e., p. 393). The response is thus clearly an avoiding 

 reaction, like that of Stentor. When the water contains much oxygen, 

 on the other hand, Paramecium bursaria avoids the light. On reach- 

 ing a lighted area the animals react in the way above characterized, 

 and return into the darkness. When they gather in light, it is especially 

 in the red rays of the spectrum that they collect; these are the rays in 

 which the chlorophyll is most active. When they avoid light, it is 

 again the red rays that are most effective in producing the avoiding 

 reaction. 



Hertel (1904) found that Paramecium bursaria, Epistylis plicatilis, 

 Stentor polymorphous, and Carchesium react to ultra-violet light, of 



