Ecological and Experimental Study of Sarcophagidce 8 1 



is evident that an error has taken place. Therefore, it does equally 

 well to apply the "Trial and Error Theory." 



The following quotation from Jennings ('05), p. 475, apparently, 

 makes little distinction, if any, between the two theories just men- 

 tioned: "We perform movements which subject us to various con- 

 ditions, till one is found that relieves the difficulty. We call the 

 process searching, testing, trial, and the like. In the lowest and 

 highest organisms the injurious condition acts as a stimulus to 

 produce many movements, subjecting the organisms to various 

 conditions, one of which is selected." 



The use of the terms "selected" and " selection ' which frequently 

 recur in the paper above quoted should not be overlooked with- 

 out a thought as to their significance. The first impression is 

 that these terms imply intelligent choice on the part of the organism, 

 but the author (Jennings) undoubtedly expects the broader inter- 

 pretation, such as expressed by the term selection when applied 

 to a magnet. This also holds equally well for the theory of the 

 ''Selection of random movements." There is in reality no intel- 

 ligent choice involved; the organism responds reflexlyto the stim- 

 ulus, either positively or negatively. 



Each of the three theories of animal behavior evidently ex- 

 plains much, but the writer believes, at least in reference to his 

 own experiments cited above and others cited below, that the 

 tropism theory is not sufficient without either the second or third 

 theory, and vice versa. It is still largely a matter of theory whether 

 animal behavior can be so readily explained. Even in fly larvae 

 we have to deal with what seems to be a death feint, and that in 

 itself leaves much to be explained. 



Phototaxis 



Observations were made on the same larvae used in the first 

 experiment. In the evening of the same day (June 30, 1905,) on 

 lighting the lamp, the larvae were noticed to leave the flesh at once 

 and hasten toward the side of the vial nearest the light. This 

 took them 4.5 cm. away from the food. Changing the angle 

 between the vial and the light or rolling the tube over always 

 resulted in a readjustment on the part of the larvae. Moving the 



