226 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



'93, Sedgwick, '94). It is interesting to compare the phenomena thus 

 observed in specimens prepared by the Davidoff method witli those pre- 

 pared by the vom Rath method, since the latter clearly differentiates 

 the nerve fibrils, and gives the clue as to the meaning of the cells 

 proliferated from the mesocephalic ganglion. Figure I is drawn from a 

 sagittal section of an embrj'o with 55 somites killed by the vom Eath 

 method, and fortunately so oriented as to show the oculomotorius in its 

 course from the inner side of the mesocephalic gan- 

 . ■ i:-- glion to a point very near the brain wall. The 



nerve itself is composed of three deeply impreg- 

 nated fibrils, which near the brain wall are closely 

 united to one another, while peripherally they be- 

 come separated. Two lightly staining cells with 

 granular pi'otoplasm lie closely adherent to the 

 nerve, and with low powers are indistinguishable 

 from it. Others appear in the process of migra- 

 tion from the mesocephalic ganglion to assume 

 similar relation. Whether these cells become ele- 

 ments of the oculomotoi'ius ganglion, which would 

 thus conform in its mode of development to the 

 type of a sympathetic ganglion,-^ or whether they 

 form the nuclei of Schwann's sheath, I am not fit 

 present in a position to state, since I have not 

 been able to trace their fate. It is of course pos- 

 sible that they contribute to both ganglion and 

 sheath. Whether cells from the mesenchyma in 

 this region contribute to both of these ends, 

 seems to me a question of not great morphologi- 

 cal importance, since in mj' opinion these cells are 

 in gi'eat measure, if not entirely, derivatives from 

 the neural crest, and thus ectodermal^ not mesodermal, in origin. From 

 the evidence thus stated it is seen that the oculomotorius must be 



1 Many investigators (Rudinger, Arnold, Gegenbaur, Scliwalbe, Hoffmann, Onodi, 

 van Wijhe, Dohrn, Beard, Ewart) have, on histological and embryological grounds, 

 agreed that this ganglion belongs to the sympathetic system. 



Fig. I. Sagittal section of a Squalus embryo with 55 somites, showing the 

 oculomotorius in its course from the mesocephalic ganglion toward the brain. 

 X 4~7- The fibrillar nerve and the peripheral nuclei may easily be distinguished. 

 cl. ms-ce., migratory cell from the mesocephalic ganglion; oc-mot., fibres of the 

 oculomotorius. 



