VERMES, FLY LARVAE, AND ECHINODERMS 199 



movement of the earthworm seems, therefore, to be nearly 

 as Hkely to be towards the Hght as away from it. The 

 shght preponderance of negative turns may be due to the 

 fact that some of the smaller trial movements were over- 

 looked, to a slight direct orienting effect of the rays, or 

 merely to chance." 



Harper (1905), working on Perichaeta bermudensis and a 

 species of Lumbricus in various light intensities, concluded 

 that in light of comparatively low intensity orientation is 

 indirect and that there are numerous random movements, 

 but in direct sunlight, especially if the worms have previ- 

 ously been kept in darkness, orientation is direct and ran- 

 dom movements are almost entirely eliminated. 



I undertook the study of the reactions of Allolobophora 

 foetida with the express purpose of ascertaining the effect 

 of constant light intensity on the rate of movement with 

 different portions of the animal highly illuminated, thinking 

 that it might be possible thus to demonstrate the difference 

 between the action of light as an orienting stimulus, and 

 a stimulus affecting the general activity of the organism. 

 The rate of movement in this form however is so irregular 

 that I found it impossible to obtain results worthy of con- 

 sideration. I therefore turned my attention to direct obser- 

 vation of the process of orientation. 



In locomotion the earthworm usually swings its anterior 

 end from side to side, but not nearly so regularly as do blow- 

 fly larvae. If after a specimen is oriented in a beam of 

 light, the ray direction is suddenly changed so as to illumi- 

 nate the side, one of four different kinds of movements may 

 result: (i) a contraction of the anterior end; (2) an exten- 

 sion of the anterior end ; (3) sudden raising of the anterior 

 end frequently accompanied by swinging from side to side, 

 or (4) direct turning either toward or from the source of 

 light in the plane of the substratum. If the animal is 

 active, the lateral movements of the anterior end are more 

 pronounced and regular during its locomotion than if it is 

 sluggish. When exposed to unilateral illumination in such 



