312 F. L. LANDACRE 



they as distinct from each other in their mode of origin as they 

 are in their structure and function in the adult? 



Even a cursory reading of the literature on cerebral nerves 

 shows a well defined movement away from the idea of concrete- 

 ness of origin and toward that of discreteness of origin. Recently 

 however, so far as I am aware, no attempt has been made to 

 follow out carefully the development of the cerebral ganglia in 

 some type in which the nerve components are known. The 

 present paper is an attempt to fill this gap in our knowledge by 

 tracing the various components back to their earliest recogniz- 

 able stages, keeping in mind the fact that the origin of a defini- 

 tive ganglionic mass of known composition and function in the 

 adult is the end in view. The attempt to account for the fate of 

 all embryonic cell masses, a part of which may go to form ganglia, 

 presents a totally different problem and one with which we are 

 unable to cope with present technical methods. 



I wish to express my gratitude to Dr. CO. Whitman for his 

 friendly criticism and guidance during the progress of this work. 



HISTORICAL SKETCH 



The following brief historical account aims to give only the 

 important advances by which our knowledge of the discrete- 

 ness in origin and structure of the cranial ganglia and nerves 

 has grown. 



According to Balfour ('75), before the appearance of his work 

 on the spinal ganglia in Elasmobranchs, it was the prevailing opin- 

 ion that the ganglia were derived from the mesoblast of the ver- 

 tebrae. His had in 1868 ascribed their origin to the epiblast but 

 his work seems not to have been confirmed up to the time Bal- 

 four published. Balfour, as is well known, traced the ganglia 

 to the cord but believed that his work diverged from that of His 

 no less than from that of his own predecessors. Goette and Sem- 

 per, writing in 1875, however, had attributed the origin of the 

 nerves to the epiblast and Goette had extended this observation to 

 the head. In 1882 Van Wijhe and Hoffmann, working on teleosts, 

 confirmed Goette's work and Van Wijhe showed that the neural 



