26 The Ohio Journal of Science [Vol. XVII, No. 2, 



is wanting, although in the study of Rana embryos by Landacre 

 and McClellan ('12) and of a Plethedon embryo by Kostir 

 in an unpublished paper summarized in Fig. 29, it was found 

 that certain ganglia, other than these two, which form com- 

 plexes in the adult stand out separate and distinct in the 

 embryo. 



The results of these studies of embryonic conditions indicate 

 a process of fusion in the ontogenetic development of certain 

 ganglionic complexes other than that of the trigeminus. As 

 stated above, it has been assumed that fusion takes place in 

 the phylogenetic development of the profundus and Gasserian 

 ganglia. So far as I know, however, the ontogenetic develop- 

 ment of these two ganglia has not been studied in a form where 

 they are separate in the embryo and form one complex in the 

 adult. 



The profundus ganglion has been found separate from the 

 Gasserian in an early embryo of Lepidosteus, (Landacre '11) 

 and distinct but not detached from the Gasserian in Rana 

 (Landacre '12) and in the 11.5 mm. embryo of Plethedon 

 glutinosus referred to above, but the exact relations of the 

 profundus and Gasserian in the ontogeny of a favorable form 

 have not been followed in detail. The present study was, 

 therefore, undertaken with the purpose of determining the 

 exact relations of the profundus and Gasserian ganglia in the 

 early ontogeny of a typical urodele amphibian, Plethedon 

 glutinosus. 



This study was preceded by that of Kostir in an unpublished 

 work on the 11.5 mm. embryo of Plethedon gl. and is an endeavor 

 to trace the profundus and Gasserian ganglia from the con- 

 dition in this 11.5 mm. embryo to earlier stages where the 

 ganglia are separate and to describe their exact relation at 

 critical stages. 



This problem has definite limitations and no final con- 

 clusions concerning the phylogenetic relations of these two 

 ganglia can be drawn from the results of this study, but if 

 similar studies were made on a sufficient number of types in 

 the vertebrate series, light would undoubtedly be thrown on 

 the fate of the profundus and Gasserian in phylogeny. 



I wish to express my gratitude to Professor Landacre for 

 the help, constant encouragement and inspiration he has 

 given me during the progress of this study. 



