Morse, Reactions of the Larva of Tetiebrio Molitor. 727 



worm is first thrown upon an illuminated area, it very frequently 

 does not immediately orient, but the head is swung from side to side 

 and up and down, and only after this is done is a definite direction 

 taken. 



Cole mentions similar observations. The chart herewith given rep- 

 resents the positions of fourteen individuals a few seconds after being 

 thrown into an illuminated area (I) and again one minute after 

 this (II). Within this time, some had moved a decimeter away 

 (number 3, for example,) while others (as number 13) had simply 

 swung in their tracks. 



In the case of unilateral stimulation made by covering the ocelli 

 of one side, we see the same testing movements. In this case, when 

 the sway is greater towards one side than the other, the path is a 

 segment of a circle. Such movements may be so compensated that 

 the path is straight. 



In many respects, the reactions of this larva are similar to those 

 described by Jennings ('06) for Lumbricus. Thus, if the larva be 

 stimulated first on one side and then on the other, one of the follow- 

 ing reactions may' occur: 



1. It may turn towards the stimulated side. 



2. It may turn away from that side. 



3. It may creep backward. 



4. It may creep forward. 



5. It may raise and lower its head and wave it about. 



These reactions may follow in the same individual or they may be 

 exhibited successively, by different worms. I have found it impos- 

 sible to correlate these variations of behavior with external factors. 



As to the method of reaction with respect to random movements 

 little can be said. At first glance, it seems evident that the orienta- 

 tion is the result of a selection of such random movements. Closer 

 study leaves one in doubt as to whether there is not something more 

 to be determined. The circling reaction is such as one would expect 

 to find if there is a mechanical response such as the theory of 

 tropisms demands. In only one case were circling movements ob- 

 served, and then only for a short time, but whether this single case 

 represents anything with bearing on the general question is doubtful. 



