338 HORACE W. STUNKARD 



grounds, but contended that the differences in observation and 

 the divergent conclusions of investigators who have examined 

 neuromeres mihtate against the confidence of Locy, Hill, John- 

 ston, Griggs, and others who hold that through the study of 

 neuromerism the primitive segmentation of the head will be 

 ascertained. Quoting Dr. Bashford Dean, he stated that in the 

 forebrain of Bdellostoma there appear two, three, or four neuro- 

 meres on one side or the other, never paired; in the midbrain 

 there is any number from one to eight ; while in the hindbrain the 

 number varies from three to twenty-four, differing in number on 

 different sides, a difference of ten having been noted in the right 

 and left sides of the same individual. He added that he had 

 examined hundreds of Squalus embryos in an attempt to con- 

 firm Locy's results, and only two or three showed symmetry or 

 regularity in the segmentation of the edges of the neural plate, 

 while the beaded thickenings were not only asymmetrical, but 

 quite variable in different specimens. He maintained that the 

 primary brain vesicles and not their secondary subdivisions are 

 homologous with the hindbrain neuromeres and that the corre- 

 spondence in number of primar}^ brain vesicles, myotomes, and 

 crania] nerves argues strongly for the metameric value of these 

 structures. 



Smith ('14) observed transverse markings in the procephalic 

 plate of Desmognathus fusca embryos which were very transient, 

 varied in position in different individuals, and w^hich he was 

 unable to trace through from one stage to another in living 

 specimens. In the posterior part of the plate the markings were 

 more uniform, persisted longer, and were subject to but slight 

 variation. In some specimens they corresponded closely to 

 the outpocketings in the medullary folds, but not in other 

 individuals. He also described plications in the medullary 

 folds which appeared early and persisted until fused and ab- 

 sorbed in the expanding prosencephalon. These lateral irregu- 

 larities did not correspond to the median grooves and he ascribed 

 their formation to mechanical factors. He pointed out that it 

 would be easily possible to select from the material a series which 

 would show a uniform development and fate of these foldings, but 



