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 
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