945 



accordingly compelled to investigate more closely tlie pobt-emUrvoiial 

 growth, especially that of the peripliei-al nervous system. 



When these investigations were planned and also during the time 

 when the greatei' part of the work was being carried out, I was 

 quite nnaccpiainted with the comprehensive American literature 

 connected with this subject, especially the publications of "The Wistar 

 Institute of Anatoujy and Biology". It is only a month since 1 learned 

 about this during a visit to the Central Institute for Brain Research 

 at Amsterdam for purposes of study. For the opportunity of doing 

 so, for the extreme kindness shown to me and for much good 

 advice and valuable criticism I wish to express my most cordial 

 thanks to Dr. Ariëns Kappkrs and Dr. B. Bhouwer. During this 

 journey 1 also stayed with Prof. J. Bokkk at Leyden and I am 

 deeply indebted to him for his exceedingly cordial reception and 

 very valuable and pertinent criticism. I am also much indebted to 

 my chief, Prof. J. Lündüren, for his kindness in revising the English 

 of the manuscript. 



The results I obtained in investigating the post-embryonal develop- 

 ment of the nervous system confirm in certain points the results 

 obtained by others, especially by "The Wistar Institute of Anatomy 

 and Biology", but on what appear to me to be the most important 

 points my results differ essentially from those of former investigators 

 of this subject. I have attempted to tind the causes of this differeiu'e 

 and have discovered that they lie in the different methods of investi- 

 gation that have been used. Previous investigators of "this question 

 worked with methods for the staining of medullary sheatiis and 

 have determined the number of medullated nerves, whereas I have 

 worked with neurotibril impregnation methods and have determined 

 the number of nerve fibres. 



Material and methods. 



The majority of the species of animals used in my investigations 

 have, as far as I can find in literature, not been previously subjected 

 to a morphological study of their post-embryonal growth. This was 

 a cause of great trouble to me. It would of course have been more 

 advantageous to use an animal that had been carefully investigated 

 before, when it was a question of explaining something that was 

 essentially new. A very convenient animal of this kind is Miis 

 fiorwegicus albinus , which has been the subject of Jinmbers of 

 detailed investigations concerning its post-embryonal growth at "The 



