30 



TROPISMS 



tions) becomes unequal. Fig. 1,B, gives the change in posi- 

 tion of the body and of the legs in the larva of a dragon 

 fly (yEschna) after the left half of the cerebral ganglion 

 has been destroyed (Matula 541 )- Such an animal moves 

 in a circle to the right. The longitudinal muscles con- 

 necting the segments of the body are under higher tension 

 on the right side of the body than on the left and the body 



Fig. 1. — B, forced position of larva of the dragon fly (/Eschna) whose left cerebral 

 ganglion is destroyed. The body is convex on the left side, due to a relaxation of the muscles 

 connecting the segments on the left side. The position of the legs is such that the animal 

 can only move in circles to the right. This asymmetry disappears again when both ganglia 

 are destroyed, C. A, normal animal. (After Matula.) 



is bent with its convex side to the left. The normally 

 symmetrical position of the legs (Fig. 1,-4) is now 

 changed in such a way (Fig. 1, B) that the animal is no 

 longer able to move in a straight line, but is forced to move 

 in circles to its right. We shall see later that similar 

 changes in the position of the legs are produced in a posi- 

 tively heliotropic insect when the left eye is blackened 

 and in a negatively heliotropic insect when the right eye 



