8o William B. H 



errns 



a point farther away from the flesh but on a line with it, and the 

 starting point of the first larva. This process required an hour and 

 four minutes and the larva died at this place apparently from 

 exhaustion. 



A fourth larva placed 3^ cm. to one side of the starting point of 

 the first also failed to find the food. Its course led it farther away 

 and finally off the paper. 



Discussion — From the above two experiments it will be seen that 

 there are two factors involved in finding the food. First, the primary 

 stimulation of the larvae by means of the food. Whatever the nature 

 of this stimulation may be, and whatsoever the internal mechanism 

 involved, the process which underlies the turning of the larva in 

 an effort to draw nearer to the food, may be termed chemotaxis. 

 The second factor is the swaying of the head from side to side or in 

 an arc of a circle. This the larva does for the purpose of orienta- 

 tion, and the process may be termed, according to Holmes ('05), 

 "Selection of Random Movements," or, accordingto Jennings ('04), 

 ''Trial and Error Movements." Both processes cover the case 

 equally well. The writer has been unable to detect any dissimi- 

 larity between the two theories, as applied to the behavior of fly 

 larvae. 



The larvae stop frequently in their course, sway the head as 

 above indicated, also circle frequently while crawling. The same 

 course may be pursued again or there may be a change in direction 

 which is generally the case after a pause. It is clear that an over- 

 production of random movements is involved; that a selection is 

 made from these, depending on the force of the stimulation, and 

 that the larvae are thus guided on their way. On the other hand, 

 it may be said that the larvae reach the food successfully because 

 they pause frequently in the course and sway the head about in 

 order to try the conditions, then when they change the course, it 



back to the food. Comparatively few found it necessary to do this, since the more direct route was 

 naturally along the lower side. 



The smallest larvae seemed to have the most trouble in reaching the food. One very small larva 

 (No. 6) remained within a distance of 2 cm. from the flesh for over an hour and a half. No larva left 

 the flesh to return to the smaller vial, though once in a while one started away, but always to return 

 in a few seconds. The lar\'as were under observation all day and all evening. 



