288 C. D. SNYDER. 



(a) The coordinating center of locomotion in the hind-legs is 

 located between the sixteenth and the eighteenth. segments of the 

 trunk. 



(&) Walking movements in the hind legs after the spinal-cord 

 is severed are due primarily not to impulses arising in the spinal 

 centers, but to impulses that arise in the sensory cells of the 

 periphery. 



(c) These sensory impulses may be produced in the skin and 

 muscles of the body-walls by stretching-stimuli ; in the skin of 

 the body-walls and of the legs by mechanical-impact-stimuli 

 (friction- or tapping-stimuli). 



(c/) The fact that Batrachoseps with sectioned cords walk on 

 their hind-legs when carried along by their fore-legs supports 

 Loeb's idea that the same thing would obtain in dogs with sec- 

 tioned cords if they could only stand up, or if their legs were 

 shorter so that they might be effective in their movements when 

 the trunk is prostrate. The difficulty in the dog is not due to 

 the absence of the walking apparatus, but to the absence of 

 "tone" in the muscles. 



(e) Perhaps the essential thing supplied by the nerve-cord, as 

 such, to the limbs during locomotion is this tone, this compli- 

 mentary resistance of the muscles toward each other which keeps 

 them ready for instantaneous regulated action, and which is prob- 

 ably maintained by impulses passing down from the organs or 

 centers of equilibrium. 



(/") If respiration could be properly maintained in the pos- 

 terior half of Batrachoseps after being severed entirely from the 

 anterior half, it is probable that walking movements could be 

 started in the hind-legs by stretching-, or friction-, or tapping- 

 stimuli, that is, by tugging gently at the front end of the posterior 

 half, or by dragging it a distance over moist blotting paper, or 

 by fastening it by means of a string to the anterior half and 

 allowing the latter (which can walk along spontaneously) to pull 

 at. or drag, the former along. 



THE R. SPRECKELS PHYSIOLOGICAL LABORATORY, 

 BERKELEY, CALIFORNIA. 



