280 G. E. COfillILL 



II. THE PHYSIOLOGICAL PAirr 

 1. Response to tactile stimulation 



Early in my study of the responses of these embryos to tactile 

 stimulation it became apparent to. me that the skin of the pre- 

 auditory region was less sensitive than was that of the post- 

 auditory region. For conclusive evidence upon this point, how- 

 ever, I am indebted to one of my graduate students, Miss Ruth 

 Orcutt, who in March, 1911 carried out a series of experiments, 

 two of which I introduce here as typical of her results. 



Ten specimens were selected which were approaching very 

 near to the typical coiled-reaction stage, their movements being 

 not quite extensive enough to be typical. These were touched 

 with a hair one after the other in regular order in the following 

 manner: At each trial an embryo was at first touched in the 

 region of the eye. If this stimulus produced a response, the next 

 embryo of the series was touched; if it did not produce response, 

 the same embryo was, after an interval, touched over the post- 

 auditory region in the territory of innervation by the vagus 

 nerve. If response occurred, the next embryo was tested; if not, 

 the same embryo was then touched over the myotomes of the 

 cervical region, the territory of the Rohon-Beard cells of the 

 spinal cord. The ten embryos were worked over in regular 

 order in this manner till one hundred forty-three responses oc- 

 curred. Of these five were in response to touch on the preaudi- 

 tory region; 66, to stimulation of the territory of the vagus 

 nerve; and 72, to stimulation of spinal territory strictly. 



Another group of embryos of a distinctly more advanced stage, 

 being in the advanced coiled-reaction stage, were tested in the 

 same manner. These gave 94 responses, of which 12 were in 

 response to stimulation of the trigeminal region; 41, to stimu- 

 lation of the territory of the vagus; 41, to stimulation of the 

 spinal region. 



These and other experiments upon this question give unequiv- 

 ocal evidence that stimuli from the spinal field reach the motor 

 centers with much greater facility and certainty than do stimuli 



