MUSEUM OF COMPARATIVE ZOOLOGY. 187 



Orr says : " Balfour described certain internal swellings of the lateral 

 wall of the hind-brain of elasmobranch embryos : ' Swellings of the 

 brain towards the interior of the fourth ventricle are in connection with 

 the first five roots of the vagus and the glosso-pharyngeal root, and a 

 swelling is also intercalated between the first root of vagus and the 

 glosso-pharyngeal root.' In his figure (Fig. 5, PI. XVI., I. c.) there are 

 no external marks of these divisions, and the * swellings ' lie opposite 

 the nerve roots while in the region between the nerve roots there are 

 internal depressions. In the lizard, on the contrary, in the region be- 

 tween the nerve roots are internal ridges. The two conditions are thus 

 very different ; but possibly younger elasmobranch embryos might show 

 a connection between these swellings and neuromeres." 1 My experience 

 with the chick leads me to believe that possibly younger stages in the 

 development of the lizard than those which either Orr or Beraneck was 

 able to study may show a connection between the " swellings " and the 

 nerve roots. 



1 Loc. tit., pp. 336, 337. 



July, 1889. 



