REACTIONS TO LIGHT IN CILIATES AND FLAGELLATES. 63 



CRYPTOMONAS AND CHLAMYDOMONAS. 



Cryptomonas ovata is one of the organisms studied by Strasburger 

 (1878), under the name Chilomonas ovata , in his classical paper on 

 reactions to light in flagellates and swarm-spores. 



The specimens studied by the present author were mostly of the 

 " young" form, having pointed, curved, posterior ends. One side is 

 strongly convex, while the other is less curved, or is even concave near 

 the posterior end. It is thus very easy to distinguish the two sides of 

 the organism and to observe their relation to the movements. 



Cryptomonas ovata swims in a rather wide spiral, with the more 

 convex side toward the outer surface of the spiral. In other words, the 

 organism swerves continually toward the more convex side. The 

 response to usual stimuli is a strong turn toward this convex surface ; 

 this is easily seen when the organism comes in contact with an 

 obstacle. 



The Cryptomonads swim toward or away from the source of light 

 under the same conditions as Euglena, and gather in lighted areas in 

 the same manner as does the organism last named. They react to a 

 sudden decrease in the intensity of illumination by turning toward the 

 more convex side. If the decrease in intensity is marked, the organism 

 turns suddenly for a long distance, 90 or more, so that the course is 

 completely changed. If the stimulus is less the turning toward the 

 more convex side is not so rapid, and since the revolution on the long 

 axis is continued the body of the organism describes the surface of a 

 wide cone or frustum of a cone. When a large number of specimens 

 react in this way at the same time a peculiar shaking or trembling 

 appearance is produced; this is evidently what Strasburger (1878) 

 called u Erschiitterung " or " Zittern." As a consequence of the wide 

 swerving, when the normal method of swimming is resumed the course 

 lies in a new direction. 



In all these respects Cryptomonas exactly resembles Euglena. Fur- 

 ther, the organism becomes oriented to light in precisely the same manner 

 as is described above for Euglena. In fact, if we substitute " more 

 convex side" for " dorsal side " in the account of Euglena, it will fit 

 almost throughout the reactions of Cryptomonas. It is therefore unnec- 

 essary to describe the phenomena in Cryptomonas in detail. 



A study was made also of the reactions of a species of Chlamydo- 

 monas. The movements of Chlamydomonas and its reactions to light 

 resemble those of Euglena and Cryptomonas. But the organism is so 

 small and the differentiations of the bodily structure are so slight that 

 I was unable to determine the relation of its structure to the spiral 

 path and to the direction of turning in the reaction. The oriented 



