GALVANOTROPISM 



39 



nervous system, while those innervating the flexors are on 

 the same side. This diagram corresponds to reality, ac- 

 cording to the histological work of Allen. When the cur- 

 rent goes from right to left through the crustacean the cell 

 bodies of the neurons on the right side are in catelectro- 

 tonus, those on the left side in anelectrotonus. The for- 

 mer are, therefore, in a state of increased "irritability," 

 the latter in a state of diminished ' ' irritability. ' ' Hence 

 the flexors of the right leg are contracted and the exten- 

 sors relaxed, while the flexors of the left leg are relaxed 

 and the extensors contracted. 



FIG. 7. Diagram indicating the orientation of the neurons for flexor and extensor 

 muscles of the right and left legs to explain changes of position of legs under influence of 

 galvanic current. (After Loeb and Maxwell.) 



Another crustacean Gelasimus 307 shows the same effect 

 of the current when it goes sidewise through its body. 

 When the thoracic ganglion from which the nerves of the 

 legs originate is cut longitudinally in the middle, all the 

 legs assume permanently a bent position, confirming our 

 assumption that the extensor nerves cross over while 

 the flexors originate from the same side of the ganglion 

 on which their muscles are. It, therefore, looks as if our 

 diagram were the expression of the actual condition. 



In the same way we can explain the results of a gal- 

 vanic current when it goes through the animal length- 

 wise. We only need to assume that the cell bodies which 

 send their fibers to the flexors of the third pair of legs 



