368 STUDIES IN GENERAL PHYSIOLOGY 



structure of the central nervous system than in lower ani- 

 mals. The fact that Planarians continue to react upon 

 light if their brain is removed, or that Ciona continues to 

 show its characteristic reaction after the loss of its ganglion 

 seems to suggest such an idea. But it would be false, never- 

 theless. The contraction of the iris of the eye, if stronger 

 light falls into the latter, is a typical reflex action, called 

 forth through the effect of the light upon the retina. If, 

 however, the reflex center is destroyed or the iris cut out, 

 an increase of the intensity of the light which strikes the 

 iris continues to cause a contraction of the iris. This fact 

 is known for frogs and eels, and I have observed it in sharks. 

 It is probably true for mammalians also. The reflex act 

 therefore may serve here, as in Planarians, for the greater 

 conduction of stimuli. 



When a dog, whose spinal cord has been cut, is lifted so 

 that its body hangs down vertically, a peculiar fact can be 

 observed, as Goltz has shown. The legs are thrown into 

 pendulum-like motions resembling walking motions. These 

 motions are produced by the passive stretching to which the 

 skin on the ventral side of the hip- joints is subjected through 

 the weight of the legs. These pendulum-like motions are 

 comparable to the reflectory contraction of the longitudinal 

 muscles of the earthworm when its skin is stretched. This 

 reflex would suffice to call forth co-ordinated walking motions 

 in the dog whose spinal cord is severed, if such a dog were 

 only able to stand on its legs. The walking motions of the 

 anterior legs would produce periodically the stretching of 

 the skin which is required for the locomotion of the posterior 

 legs. The difference in the behavior of a dog with severed 

 spinal cord and an earthworm with severed ganglionic chain 

 in regard to co-ordinated locomotion is therefore less deter- 

 mined by the differences in the function of their central 

 nervous system than by differences in the structure of their 



