CoGHil.i., The Reaction to Tactile St/i/iiil/. 85 



I believe, relatively rare. K(ir iiislaiiee, wlieii the stimulus is 

 applied to the under side of the head as the animal lies on its side, 

 and the response is a moxcment of the head awaj frnni the side 

 touched, it is inconceivable that this response is to a direct pressure 

 upon the muscles effectino- jho moveuKint, and it seems altoo-ether 

 ipiprobable that such a stimnlus could be brought to bear upon the 

 central nervous system directly in such a mauncu- as to give rise to 

 a constant form of response. Or, in case the stimulus is applied 

 to the margin of the dorsal or ventral caudal fm and a movement 

 of the head only results, as regularly occurs in certain phases of 

 development, it is absolutely impossible for such a reaction to be 

 given in response to pressure either upon the acting muscles or upon 

 the central nervous system. As reactions of this sort occur here 

 and there throughout nearly every one of my experiments, it seems 

 to me certain that the stimulus employed was, with possibly rare 

 exceptions, purely tactile, and that, so far as the mode of stimulation 

 is concerned, my conclusions are valid. 



Ordinarily the stimulus was applied to the upper side of the 

 specimen as it lay on its side on the bottom of the dish„ Frequently, 

 however, it was applied to the under side of the specimen from 

 beneath, in order to determine whether contact with the dish had any 

 influence on the mode of reaction, but it was impossible to detect 

 any factor of this kind in the responses. Some embryos, also, were 

 suspended in an upright position and tested for the same purpose, 

 and with the same result. 



An individual record in detail was kept of each eml)ryo froui the 

 time it was removed from the egg membranes till the end of the ex- 

 periment. In the record of each trial, or a])plication of the stim- 

 ulus, the following factors were noted partieuhn-ly : the region and 

 side touched, the form of the response and the time of the trial. 

 Tabulated schemes for rapid recording were tried in my first experi- 

 ments of 1906, but it soon became apparent that such forms could 

 not be adhered to, for they were necessarily based upon presump- 

 tions of some sort and were, therefore, a hindrance rather than a 

 help to alert observation. These methods were wholly abandoned 

 and have no part in the records from which this paper is written. 



