324 Robert J. Terry. 



the Harvard Embryological Collection by an extensive series of 

 sections of embryonic and larval stages. In addition, the brains 

 of specimens half and fully grown were obtained and prepared for 

 dissection and microscopical study. Other fishes included in the 

 research are Salvelinus, Fmidulus, Ameiurus, Lepidosteus, Amia, 

 Acanthias and Petromyzon. 



I Description 



Opsanus Embryos of 11 mm. in Length 



Epiphysis. In embryos of this stage the epiphysis is located 

 in the middle of a depression intervening dorsally between the mid- 

 brain and telencephalon (fig. 1, ES) . Its direction is nearly dorsad, 

 corresponding in this respect with the posterior epiphysis of Salmo 

 embryos of 7mm. Hill ('94) found the posterior epiphysis in larval 

 salmon of 13 mm. directed forward, so that it presented dorsal 

 and ventral surfaces. The end of the organ lay close to the epi- 

 dermis, whereas in Opsanus it reaches a level half-way between 

 the diencephalic roof and the ectoderm. Differentiation of the 

 outward form has already begun and sagittal sections (fig. 2, E) 

 show an ovoid end-vesicle surmounting a cylindrical stalk. The 

 latter expands at its base where it joins the diencephalic roof, and 

 presents a slight curve in the sagittal plane in adaptation to the 

 superior commissure lying just anterior. The epiphysis of Opsanus 

 at the present stage, like that of Clupea (Holt '91), is a solid 

 structure. These teleosts differ, therefore, from the embryos of Salmo 

 in whi ch, as shown by Hill, the epiphysis is hollow. Sections of the 

 solid epiphysis give evidence, however, of a difference in the 

 the structure of the peripheral and central regions, the former 

 appearing deeply, the latter but lightly stained. Moreover the 

 protoplastoi of the peripheral coat is nucleated, whereas that of 

 the central region is non-nucleated. ^ This sort of structure is 



2 There are no cell boundaries in the protoplasm of the epiphysis at this stage; 

 the organ has a syncytial structure and the nuclei are all located in the peripheral 

 parts, forming a more or less even layer. 



