536 Stewart Paton 



that functional events may, without qualification, be expressed by 

 the same signs and Symbols as tliose employed by the morphologist. 



The last word ui)on these borderline questious will undoubtedly 

 come from the physicist aud chemist, but the work of preparing the 

 way for them is still carried on in a field from which the Student 

 of morjihology and histology may not yet be excluded. 



As far as possible, in recording events and eonditions, a form of 

 parallelism has been followed in order to facilitate description and 

 to avoid any implied acquieseence in purely theoretical considerations. 

 It must be understood, however, that this form of parallelism is 

 provisionai and relative, and therefore quite distinct from that fre- 

 quently adopted as a philosophical creed by many physiologists 

 when discussing the relations of structure and function in the ner- 

 vous system. 



The attempt has also been made to describe the results of 

 these observations as objectively as possible and appreciating the 

 well merited sympathy expressed by Balfour, for the student of 

 modern scientific literature, in the Preface to his classical work 

 on the Elasmobranchs, to refer to the work of others only when the 

 occasion seems to call for it, and therefore a sufficient reason exists 

 to justify any additional tax being imposed upon the reader's atten- 

 tion and patience. 



In Section 1 a description of some of the primitive physiological 

 reactions of the embryo to its environment, to incldent Stimuli, 

 and to metabolic processes is given, while in Section 2 there is a 

 general outline of the development of the nervous system at certain 

 epochs, followed by a discussion of what seems to be the more 

 important histological characteristics of these periods; and finally 

 the attempt is made in a few instances to indicate the hearing that 

 these detachcd and isolated facts have to each other. In Section 3 

 the technical methods employed in the study of the tissues are de- 

 scribed in detail. 



Section 1. 



The observations in the main have been conducted upon the 

 embryos of Ämblystoma mexicanum, Salamaiidra maculata, Rana, 

 Salmo fontiìialis, Pristiurus melanostomus , Scyllium canicula and 

 stellare, Torpedo marmorata and ocellata, and upon a few specimens 

 of Amphioxns. As the records of results obtained in the study of 



