THE NERVOUS SYSTEM OF AMPHIBIA 289 



region, where the general cutaneous system is more precocious, 

 the connection of the lateral line nerves with the skin becomes 

 readily recognizable earlier than in the case of the general cutane- 

 ous nerves, and throughout the period under consideration the 

 lateral line nerves have the more intimate and the more exten- 

 sive contact with the skin. Judged upon the anatomical basis, 

 therefore, the lateral line system would certainly be held as play- 

 ing a larger role in the life of the organism at this time than do 

 the general cutaneous nerves. I have been unable, however, to 

 discover what this function may be and have further experiments 

 planned. 



The auditory organ, being a simple dilated vesicle, gives no 

 evidence of being a mechanism that would be adapted as a 

 receptor to the function of equilibration, so that the auditory 

 nerve, which has established quite extensive relations within the 

 brain and intimate contact with the vesicular epithelium in the 

 early swimming stage probably does not enter into the reactions 

 of the organism till a later period. As is well known, the embryos 

 of this stage lie on the side while at rest and hold the upright 

 position only during locomotion. The embryos which I select 

 as representing the early swimming stage move upon the sub- 

 stratum, and their ujoright position during locomotion is prob- 

 ably the result of the lateral thrust of the head, which would 

 tend to prevent them from settling down on either side till 

 motion ceases. 



6. Summary 



a. The j^reauditory portion of the ganglionic general cutaneous 

 system develops far in advance of the postauditor}' portion. 

 The former becomes a factor in quick and certain response only 

 about the time the embryo begins to swim, although response 

 to preauditory stmiulation occurs irregularly and infrequently 

 for a considerable time before this. 



b. The entrance of the receptor field of the trigeminal nerve 

 into function as an important factor in the behavior is closely 

 correlated with the extension of the root fibers of the trigeminal 



