DO BLOW FLY LARV.E RESPOND TO GRAVITY? 



S. O. MAST. 



Referring to the fact that blow-fly larvse crawl under objects 

 in water just as they do outside, Loeb says (1905, p. 68):' "In 

 these experiments I was struck by the fact that the animals, 

 when placed under the surface of the water, do not swim upward 

 and so avoid death, but swim downward. I cannot explain this 

 fact. Under other conditions positive geotropism cannot be 

 demonstrated in these animals." Relying on this statement of 

 Loeb, I attempted to ascertain the cause of the expressed dif- 

 ference in response to gravity of fly-larvae in air and in water 

 and the method of orientation in swimming downward. The 

 result of this investigation follows. 



In making observations on the reactions of blow-fly larvae in 

 air, twenty-five active specimens varying in length from 5 to 

 17 mm. were put into a glass jar with vertical walls so situated 

 that the light intensity in the jar was very low and approximately 

 uniform throughout, thus eliminating its influence on the direc- 

 tion of movement. In the course of several minutes it was 

 found that nearly all the larger specimens were crawling almost 

 straight upward on the sides of the jar, apparently responding 

 negatively to gravitation. The smaller larvae however crawled 

 about in all directions, horizontally and downward as well as 

 upward. What is the cause of this difference in the direction' 

 of locomotion? 



Careful observation soon showed that while most of the larger 

 larvae observed at any given time were directed upward, they 

 frequently turned and started in other directions, but that as 

 soon as they got into a position approaching the horizontal they 

 either fell to the bottom of the jar or the posterior end swung 

 downward somewhat every time it was raised in the process of 

 looping, and that this resulted in orientation with the anterior 

 end directed upward. 



Thus it is clear that there is no evidence of a reaction to gravi- 

 tation in these forms under the conditions of these observations, 

 i. e., in air. Do they become positive to gravity in water and 

 swim downward as Loeb says, and if so, how do they orient? 



Larvae approximately 6 mm. long were taken from carrion 



' Studies in General Physiology, Vol. I., 423 pp., Chicago. 



191 



