Holmes, Random Movements. 99 



al theory we have referred to. It might be assumed, in the 

 earthworm, for instance, that light causes a greater contraction 

 of the longitudinal muscles on the less illuminated side, or that 

 it inhibits the action of the longitudinal muscles on the side 

 that receives the greater stimulus, or that both these effects are 

 combined. The attempt was made to get some clue to the 

 method of orientation by carefully watching the movements of 

 the animals under the influence of light. It soon developed 

 that what seemed at first a forced orientation, the result of a di- 

 rect reflex response, is not really such, but that the orientation 

 which occurs and which is often quite defim'te is brought about 

 in a more indirect manner by a mode of procedure which is in 

 some respects similar to the method of trial and error followed 

 by higher forms. 



The response of the earthworm to light has been noted by 

 several observers Hofmeister,^ Darwin,^ Graber,^ Yung,^ 

 Hesse,' Parker and Arkin,*^ Smith, ^ and Adams. ^ While all 

 parts of the surface of the earthworm are sensitive to light the 

 directive influence of light, as Parker and Arkin have shown, 

 is greatest at the anterior end of the body and diminishes to- 

 wards the posterior end. The negative reaction of the earth- 

 worm becomes less as the intensity of the light is diminished, 

 and in very weak light the reaction, according to Adams, be- 

 comes slightly positive. The directive influence of light was 

 tested by Parker and Arkin and by Adams by placing the 

 worm at right angles to the direction of the rays and noting the 

 number of times it extended its head towards or away from the 



'HoFMElSTER, W. Die bis jetzt bekannten Arten aus der Familie der Re- 

 genwiirmer, Braunschweig, 1S45. 



'^Darwin, C. The Formation of Vegetable Mould through the Action of 

 Worms, with Observations of their Habits, Netv York, 1900. 



•''Graber, V. Grundlinien zur Erforschung des Helligskeits und Farben- 

 sinnes der Thiere, Leipzig, 1884. ' 



*YUNG, E. Compt. Rend. Trav. Soc. Helv. Sci. Nat. l8g2, p. 127., 



^Hesse, R. Zeit. 7uiss. Zoo/. 1896, 61, 393. 



^Parker and Arkin. A/n. Jour. Physiol. 1901,4, 151. 



■'Smith, A. C. Am. Jour. Physiol., 6, 459. 



*Adams, G. p. Am. Jour. Physio!., 9, 26. 



