THE EARLY DEVELOPMENT OF THE EPIPHYSIS 

 AND PARAPHYSIS IN AMIA. 



By A. C. Eycleshymer and B. M. Davis. 



With Plate VII. 



Recent researches indicate that the solutions of certain 

 problems connected with the early development of the epiphy- 

 sis and paraphysis are to be approached through a study of the 

 early history of these structures in Fishes. Thus far little has 

 been written concerning their early development in Ganoids. 



Balfour and Parker describe and figure the early stages in 

 the development of the epiphysis in Lepidosteus, It arises as 

 a single, median, posteriorly directed outgrowth from the an- 

 terior portion of the thalamencephalon. Beyond the fact that 

 the outgrowth is at first directed backward there are no points 

 which claim special attention. 



Salensky figures an early stage of the epiphysis in Aci- 

 penser ruthenus as a single, median, posteriorly directed out- 

 growth from the roof of the thalamencephalon. 



Kupfifer describes and figures the early development of 

 both the epiphysis and paraphysis in Acipenser sturio. The 

 epiphysis is first defined in an embryo of about 57 days as a 

 single, median, posteriorly directed outgrowth. The distal part 

 of this conical evagination is soon converted into a vesicle, 

 while its proximal portion gives rise to the stalk. The para- 

 physis first appears in an embryo of about 64 hours as a slight 

 evagination in the posterior portion of the roof of the prosen- 

 cephalon. It soon assumes the form of a vesicle which at the 

 end of the larval period sends off a number of diverticula. 



Hill studied certain larval stages of Amia calva (10-15 

 mm.) and described three outgrowths from the roof of the 

 the brain. Two of these were found to arise from the roof of 

 the thalamencephalon, but Qwing to lack of material the author 



