THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 199 



the relation was not constant the usual distance was about five 

 times as far in the former field (fig. 9 and 10). 



Mast ('07) found that Volvox, which is positively phototatic, 

 was deflected toward the more strongly illuminated side in graded 

 light and concludes (p. 141) that "The direction of motion in 

 Volvox exposed to light is consequently regulated by the intensity 

 of the light on opposite sides of the colonies regardless of the diiec- 

 tion of the ray." This conclusion, as Mast shows, is in direct 

 opposition to the statement made by Loeb ('05) and already 

 referred to. 



From the experiments already enumerated and others to fol- 

 low {B), it becomes quite evident that the results obtained with 

 sarcophagid fly-larvae are quite in accord with Loeb's ('05) con- 

 clusions, and that the statement made by Mast ('07, p. 136) is 

 quite apropos at this juncture. "Let it be clearly understood 

 that in the criticism of Loeb's conclusions, I do not wish to inti- 

 mate, that because the reactions of Volvox or any other organism 

 do not take place in accord with those conclusions, they neces- 

 sarily cannot hold for the organisms Loeb worked with."^ Mast's 

 further statement on the same page in reference to that investi- 

 gator's results is, however, equally applicable, viz. "I do, however, 

 wish to state and emphasize that in my opinion his experimental 

 results as quoted above, do not warrant his conclusions, even for 

 the animals worked on, much less for all organisms which orient 

 to light." 



B. Directive graded light. A field of light, directive with 

 reference to the larvae, graded to higher intensities in the direction 

 of the ray was produced in the manner already explained. The 

 field (AB, fig. 11) was 36 cm. in length and 25 cm. in width, pro- 

 viding ample room for long journeys under these conditions. The 

 grading was from the point A, with an intensity of less than 1 

 CM., over a distance of 36 cm. to a point B, with an intensity of 

 66 CM. The larvae were started about 2 cm. beyond the point 

 A, where orientation away from the light took" place. Locomo- 



* Loeb's conclusions, were based on results obtained from experiments on 

 blow-fly larvae among other species (Loeb, '90, pp. 70-71). 



