132 H. V. NEAL 



Ziegler ('08) and his pupil Brohmer ('09) have recently at- 

 tempted to determine the number of cranial metameres, ignoring 

 the neuromeric segmentation. Is neuromerism a matter of no 

 consequence to the student of head morphology? 



6*. Are neuromeres satisfactory criteria of the primitive metamerism 



of the head? 



By his discovery of symmetrical cross furrows on the widely 

 expanded neural plate of Salamandra atra embryos von Kupffer 

 became the first exponent of the view that the nervous system 

 manifests a 'primary metamerism,' independent of the meso- 

 dermic segmentation. He was the pioneer — as he was in many 

 other lines of morphology — among those who lay stress upon 

 the segmentation of the nervous system as the best preserved 

 manifestation of the primary metamerism of the vertebrate body. 

 Repeated confirmation of the presence of neural segments prior 

 to the appearance of mesodermic segmentation has been given 

 by Froriep ('91, '93), Locy ('95), Hill ('00), Johnston ('05), 

 Wilson and Hill ('07) and Griggs ('10). 



At the same time it is a truism of morphology that the seg- 

 mentation of the nervous system is a secondary one, determined 

 by and dependent upon the segmentation of the muscular sys- 

 tem. This has been especially emphasized by Mihalkowitz ('77), 

 Ahlborn ('84 b), Froriep ('92), Kingsley ('12) and Coghill ('13). 

 Observation, however, seems to have warranted the generaliza- 

 tion that the nervous system is most conservative. When once 

 it has acquired a segmentation adapted to whatever peripheral 

 system, the segmentation is retained, even after the associated 

 structures, sensory or muscular, have disappeared. So that when 

 it was demonstrated beyond a doubt that the hindbrain neuro- 

 meres manifest a segmentation which could not be interpreted 

 upon purely mechanical grounds and which appear independ- 

 ently of the mesodermic segmentation, the conclusion seemed 

 inevitable that in these hindbrain neuromeres is preserved the 

 indisputable remnants of the primary segmentation of the head. 

 Finally when Locy ('95) claimed to have been able to trace the 



