The Nervous System of Amblystoma. 433 



Kupffer's first and second mesencephalic neuromeres, however, 

 are evidently the same as Locy's. Kupffer, as has already been 

 stated, considers these divisions described by Locy and himself 

 as of secondary origin and not true primary neuromeres, main- 

 taining that the true neuromeres are the large divisions in the 

 open neural plate which he has described as being apparent 

 in some forms of amphibians. 



Neal ('98) is the severest critic of the theory of neuromeres as 

 developed by Hill and Locy. After an investigation of Acan- 

 thias, the same form which Locy used, he disagreed with Locy 

 both as to observation and interpretation. He found that 

 ''the lobes on the opposite sides of the plate do not correspond 

 in number or position, neither do they show any definite rela- 

 tions to the mesodermal somites," and ''there is no constancy 

 in different individuals." He found these apparent segments 

 transitory and was unable to find any relation between them and 

 the later ventral segmentation of the neural tube. He pointed 

 out another apparent inaccuracy in Locy's work in that "the 

 line which separates the expanded cephalic plate from the region 

 posterior to it marks the posterior boundary of the auditory 

 invagination," instead of lying "just in front of the point where 

 subsequently the vagus nerve begins" as Locy saw it. From 

 this he concludes that Locy can not have traced his so-called 

 neuromeres correctly into the later divisions of the brain. 



Neal accepts Orr's criteria of a neuromere but he adds the 

 following important point — " the best criteria are such as associate 

 the supposed neuromeres metamerically with other structures 

 known to be segmental." Judged by this standard he con- 

 cludes that the fore-brain and the mid-brain represent each 

 one neuromere, the former being associated with the anterior 

 head cavity of Piatt and the sensory olfactory nerve, and 

 the latter with Van Wijhe's first somite and the ophthalmicus 

 profundus of the fifth nerve. Neal's method is undoubtedly 

 very valuable in showing positive evidence in favor of the pres- 

 ence of true neuromeres in the hind-brain, but it is very difficult 

 to apply so severe a test to the mid-brain and the fore-brain 

 because it has been demonstrated so clearly that the nerve com- 



