124 CHARLES EUGENE JOHNSON 



the prechordal plate below. The mesodermal wings differ from 

 the surrounding head mesoderm in that their cells are more 

 densel}'' packed. In some sections the cells in the lateral region 

 of the wings are otherwise arranged. There appears here a 

 small cavity, around which the cells are radially placed. Such 

 a structure, according to Oppel, is a characteristic somite. 



The cell-stalk which extends from the somite to the midline, 

 Oppel calls the 'Stiel,' and its length, according to him, permits 

 the somite to lie at some distance laterally behind the optic vesi- 

 cle. The somite portion differs from the corresponding somite 

 found by Hoffmann in Lacerta, in that it is sharply marked off 

 from the 'Stiel' or connecting-stalk. 



A short distance anterior to the auditory vesicle, at the side 

 of the hindbrain, Oppel found the homologue of the third head 

 somite of selachians as a mass of cells arranged radially about a 

 small cavity. On the cranial border of this soixiite, seemingly 

 growing out from it, he observed a smaller rather indefinite 

 cell-mass, which he interprets as corresponding to the anterior 

 of the two somitic structures found at this place in Lacerta by 

 Hoffmann. The structures here were not separate and distinct 

 from each other as in Lacerta, and Oppel was unable to add to 

 the suggestion as to their significance. 



Regarding a second head somite in Anguis, Oppel is less cer- 

 tain. In an embryo of eleven segments, however, a short dis- 

 tance caudad of the first head somite and somewhat nearer the 

 midline, he found a small structure which answers the require- 

 ments of a typical somite. OppeFs figure shows it in section as 

 having a well defined epithehal wall, one cell deep, enclosing a 

 small but distinct lumen. It has no connection with any other 

 structure, and a similar body occurs also on the other side. In 

 an embryo of thirteen segments he found only a small heap of 

 cells at this place, and in older specimens no further trace of it 

 was found. He could establish no connection between this 

 somite-like body and the later appearing M. obliquus superior. 



The Lacertilia have been investigated also by Corning ('00). 

 His observations were made upon embryos of Lacerta muralis 

 and L. viridis, two forms representing essentially like conditions. 



