No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 399 



Concerning the significance of these structures it can only 

 be said that from our knowledge of the organ in other groups 

 we should scarcely be warranted in considering them of phylo- 

 genetic importance; yet it cannot be said that these peculiarities 

 are without hypothetical interest. 



13. Paraphysis and Epiphysis in Amblystoma. 



From the numerous late researches it seems probable that in 

 most forms there are at least two median outgrowths in the 

 roof of the encephalon. 



The posterior of these, the epiphysis, arises according to the 

 majority of observers, among whom I may name Beraneck ('87), 

 Strahl and Martin ('88), Fran^otte ('88), Selenka ('90), and 

 Klinckowstrom ('93), as a median unpaired evagination in the 

 roof of the thalamencephalon ; this structure soon gives rise to 

 a secondary, the parietal vesicle or pineal eye. 



Others hold that instead of considering one of these vesicles 

 as secondary they are to be considered as the representatives of 

 two homodynamous structures, Leydig ('90), Hill ('9l), Locy 

 ('93). 



Again there is found a group of several vesicles arising in 

 this region, Duval and Kalt, Prenant, and others. 



The anterior, or paraphysis, generally arises slightly anterior 

 to the line which marks the boundary between prosencephalon 

 and thalamencephalon. Concerning the fate and function of 

 this organ there is much difference of opinion. Frangotte ('88) 

 derives from it a portion of the future choroid plexus. Selenka 

 ('90) suggests that it may be the rudiment of an ancestral ear, 

 while Leydig ('90) finds, instead of a single vesicle, a group of 

 five which later come into such close relation to the epiphysis 

 that Spencer ('84) figured both as one structure. 



In a brief preliminary ('92) I showed the epiphysis and para- 

 physis to be entirely independent structures in Amblystoma. 

 In the following pages I repeat the principal facts : 



The first trace of the epiphysis is in a 5 mm. embryo where 

 it shows, in section, as a crescentic evagination in the roof of 

 the thalamencephalon. The lateral walls are formed of several 

 layers of cells, while the dorsal, which comes directly in con- 



