The Nervous System of Amblystoma. 477 



General Conclusions 



The foregoing description, whatever may be the value of the 

 results attained, emphasizes the value of breaking away some- 

 what from the traditional methods of attacking the problem of 

 cephalogenesis. Two new lines of work have been followed. 



First. The number of neuromeres is not the all important 

 part of the problem. Since the time of Goethe students of 

 cephalogenesis have bent their energy mainly to finding out- how 

 many segments the head contained. Even if the search had led 

 to a definite result, which has been far from the case, the main 

 problem is far from being solved. The grouping of neuromeres 

 into tagmata may prove to be more important than the mere 

 number involved which may possibly vary. Johnston's theory 

 of longitudinal zones is a welcome breaking away from the old 

 method of counting neuromeres, and a study of germinal grooves 

 and optic lobes may prove to have still greater value. 



Second. Very early stages should be used for study. Impor- 

 tant structures appear and disappear before the formation of the 

 conventional neuromeres. This point has all along been main- 

 tained by Kupffer who has claimed that the only true primary 

 neuromeres must be sought for in the open neural plate. It 

 is evident in spite of all the recent investigation of the closing 

 and closed neural tube that there is yet a broad field for study 

 in the open plate and its allied structures. 



"The results obtained by these two new methods, so far as the - 

 bearing of the minor points of interest is concerned have already 

 been discussed along with the descriptive part of this paper. 

 It now remains to consider the general bearing of these results 

 upon the wider problem of cephalogenesis. It will be convenient 

 to employ the heading's used by Locy ('95) in his historical survey. 



First. "The primitive condition of the nervous system of 

 vertebrates." The evidence presented in this paper supports 

 the view that the nervous system of ancestral vertebrates was 

 not a simple but a complex one. In the history of Amblystoma 

 embryos a glimpse is afforded into conditions and processes which 

 must have been developed before the evolution of modern verte- 



