ii8 Journal of Comparative Neurology and Psychology. 



Nine Millimeter Stage. — Between the vagus ganglion and 

 the second spinal nerve, at this stage, sympathetic cells are 

 seen scattered in the mesoblast dorsal and internal to the aorta 

 (double). These cells are round or slightly elliptical in shape, 

 have a granular appearance, and are devoid of processes; they 

 stain a little more deeply than connective tissue cells, and usu- 

 ally are very easily distinguished from them. At places, espe- 



Fig. I. — Transverse section of 9 mm. toad, through the ganglion of the sixth 

 spinal nerve (see Fig. 7), showing the sympathetic ridge, Ri. (The section 

 passes through the extreme anterior end of the kidney on one side and just an- 

 terior to the kidney on the opposite side.) Ao. /., Aorta (median dorsal). B. P^., 

 blood-vessel. C/i., notochord. A'., kidney. Afti., mass of cells between aorta 

 and kidney or aorta and Wolffian duct. Jlfns., muscle. /?t., sympathetic ridge. 

 JV. D., Wolffian duct. X 246. Camera Lucida. Reichert, oc. 2, obj. 7 a. 



cially in the immediate region of the first and second nerves, 

 these cells are becoming aggregated to form a cord (Fig. 7, Sy.^, 

 which, in cross section, appears very irregular, and shows from 

 three to twelve cells in one section. (Fig. 2. Sy. shows a little 

 later stage.) This cordis the beginning of the differentiation of 

 the sympatJietic i?t this region. It becomes continuous back of 

 the second nerve with the ridge already mentioned. 



The mass of cells between the aorta and the Wolffian duct 



