Neal. — Nervous Syst. Squalus. 



PLATE 9. 



Stages in the development of the abducens nerve. All the specimens were 

 killed witli Davidoff's fluid (corrosive-acetic). All Figures are from frontal sections 

 except Figure 65. 



Fig. 62. A frontal section of an embryo with G2 somites (9 mm.). Magnified 450 

 diameters. Two roots are present. 



Fig. 63. From an embryo with 68 somites (10 mm.) magnified 285 diameters. 

 The course of the nerve is very direct in this stage, at least in the 

 specimen figured. Throughout the most of its course it is entirely 

 free from nuclei. 



Fig. 64. A combination from 7 sections of an embryo with 80 somites. Three 

 roots present on the side of tlie embryo figured. Deeply staining nuclei 

 appear in close connection with the nerve, and there is some (in my 

 opinion doubtful) evidence of the migration of nuclei to or from the 

 neural tube. Peripherally the nerve divides into fine fibrillae. Magni- 

 fied 200 diameters. 



Fig. 65. A cross section of an embryo with 75 somites in the region of the 

 posterior root of the abducens, magnified 285 diameters. Evidence of 

 migration of nuclei (1). 



