535 



The Eeactions of the Vertebrate Embryo to 



Stimulation and the Associated Changes in the 



Nervous System. 



By 



Stewart Paton 



Baltimore. 



With one text-figure and plates 23—25. 



The observations reeorded in the foUowing pages ave the re- 

 sults of a series of studìes begun several years ago with the in- 

 tention of describiug, as hriefly as is consistent with a(?curacy and 

 clearness of statement, some of the more important of the earliest re- 

 aetions of the embryo to Stimulation, and then noting in a parallel 

 column the synchronous morphological changes in the nervous system. 



As every investigator knows, who has attempted to solve any 

 of the Problems involving a discussion of the reciprocai relations of 

 structure and function, the difficulties , both real and fìctitious, that 

 interfere with such au undertaking, are manifold. In order to avoid 

 the dangers of speculation the attempt has been made in common 

 with Jennings (Behavior of the Lo wer Organisms, Columbia Uni- 

 versity, Biological Series 10, 1906) and other investigators, to study 

 organisms as "masses of matter". 



The present aim has been to try to describe some of the more 

 striking phenomena that occur in the embryo at the time when the 

 first cardiac beats and earliest responses to external Stimulation 

 begin, and then to determine in a general, but not specific way, 

 how far these reactions are dependaut upon the functional activity 

 of a nervous system. This problem is essentially different from the 

 far more difficult task of trying to determine the links between the 

 two sets of facts. Every efifort has been made to make use of a 

 phraseology that will not convey to the mind of the reader the idea 



