DEVELOPMENT OF THE EPIPHYSIS IN 

 COREGONUS ALBUS. 1 



F;#.I. 



CHARLES HILL. 



Through the papers of Leydig ('90), Selenka ('90), and 

 Hoffmann ('85), the evidence is accumulating that we have at 

 least two outgrowths from the roof of the embryonic brain in 

 the region where we have here- 

 tofore found only the single 

 epiphysial outgrowth. The evi- 

 dence is further strengthened 

 by the discovery of the second- 

 ary parietal vesicle described in 

 adult forms byWiedersheim 

 ('80), Ahlborn ('83), Beard ('89), 

 and Ritter ('91). In view of the 

 prevailing uncertainty as to the 

 homology of these two out- 

 growths, and as to their rela- 

 tion to the roof of the brain and 

 to one another, it has seemed to 

 me advisable to communicate 

 some observations on the sub- 

 ject that have been made inci- 

 dentally while working on the 

 primitive segmentation of the 

 brain of Coregomts alb?is (Giinth). 



In Coregonus 2 there are two epiphysial outgrowths from the 

 roof of the primary fore-brain. These may be best seen in a 

 sixty-day embryo (7 mm. in length). In Fig. I. there is shown 

 the anterior part of a living embryo at this stage, as seen from 



1 Work from the Zoological Laboratory of the University of Michigan, under the 

 direction of Professor Jacob Reighard. 



2 I desire to acknowledge my indebtedness to the Michigan State Board of Fish 

 Commissioners for a liberal supply of material. 



503 



Fig. I. — Anterior portion of em- 

 bryo, 7 mm. long, of Coregonus alius. 



