The Pineal Region in Teleosts. 333 



jecting above the surface. The center of the mass consists of 

 clear protoplasm, the whole structure bearing a close resemblance 

 •to the epiphysis of the 3.5 mm. embryo (fig. 8, A). This small 

 bud is evidently the beginning of the anterior rudimentary epi- 

 physis noted in the 11 mm. embryo. The examination of Salve- 

 linus embryos, resulted in, the discovery of two epiphyses as was 

 anticipated in view of their presence in Salmo. They are repre- 

 sented in transverse section in fig. 9. It will be seen that these 

 bodies are of unequal size, that the larger one is located in the 

 median plane and the smaller one to the left. A cavity is present 

 in the larger epiphysis. 



Hill and other investigators have remarked upon the absence 

 of mesodermal tissue between the epiphysis and ectoderm in 

 very young teleost embryos. This condition was observed in the 

 present study in the embryos^of Salvelinus (fig. 10), Fundulus, and 

 also Amia (fig. 11). It is not so however in Opsanus embryos, 

 for there is always present between the brain and the epidermis a 

 continuous layer of mesenchyma. Within this tissue the end of 

 the epiphj^sis is to be seen (fig. 7, E). It is worthy of note that, 

 whereas the end vesicle of this organ is pressed closely against 

 the epidermis in the above named fishes, it is farther removed in 

 Opsanus. A large blood sinus, lying between the superior com- 

 missure and the mesenchymal layer, is in contact with the anterior 

 surface of the epiphysis. 



Superior Commissure. It is at this stage of development that 

 the superior commissure first appears as a clearly defined bundle of 

 fibers. Its position relative to the epiphysis is the same as in the 

 11 mm. embryo. Sagittal sections show that the fibers are in- 

 completely separated by a range of nuclei into dorsal and ventral 

 groups.^ In fig. 7, it will be observed that the commissure lies 

 upon the ependyma of the post-velar arch. 



Posterior Commissure. Excepting that the fibers of the com- 

 missure are spread to a relatively greater extent upon the epi- 



' Transverse sections reveal an intermingling of certain of the ependymal cella 

 with fibers of the commissure, a condition interesting in connection with Mrs. 

 Gage's ('95) observation that, in Diemyctyius, processes of the endymal cells 

 traverse the commissure. 



