The Pineal Region in Teleosts. 335 



Velum Transversum. The transverse fold and median lobe are 

 both present, the extent and relations of the former being the same 

 as in the 11 mm. embryo. Differentiation in the form of the 

 middle lobe has not begim; its surface is smooth and it is connected 

 directly with the transverse fold. 



Paraphysis. There is no paraphyseal evagination at this 

 stage. In its place the brain-roof forms a low arch or dome, 

 sharply defined laterally and anteriorly. This paraphyseal arch 

 rises somewhat above the general level of the fore-brain tela, 

 with which it contrasts in its thicker and more deeply staining 

 epithelium. Caudally the arch goes over into the transverse 

 fold of the velum. 



Opsanus Embryos 5 mm. in Length 



Epiphysis. Instead of the more or less conical, projecting 

 epiphysis observed in the preceding stages, there is now present 

 a simple, arch-like evagination of the diencephalic roof (fig. 12, 

 EA). The middle of this arch is differentiated both in form and 

 structure from the rest (fig. 12, E). It is raised slightly above 

 the general level and presents in sections the same structural divi- 

 sions, peripheral and central, as were found in the epiphysis 

 of the older embryos. The arrangement of the nuclei in a super- 

 ficial layer is interesting in connection with Eycleshymer's ('92) 

 observation of the migration of nuclei in the epiphyseal evagina- 

 tion of Amblystoma embryos and of a somewhat similar pheno- 

 menon in the optic vesicles. The epiphyseal arch occupies the 

 median plane, its summit lying within the mesenchyma which 

 now fills the interval between the brain-roof and the epidermis. 

 The latter presents no special features in this region. A second 

 epiphj^seal outgrowth was not observed and so it appears that 

 this smaller bud is a later development than the principal epiphy- 

 seal organ. In Acanthias, a projection into the ventricle, seen 

 in sagittal sections, marks the site of the future superior commis- 

 sure and limits the epiphyseal arch anteriorly. Since this pro- 

 jection is not well defined in Opsanus, the arch goes over without 

 sharp limit into the post-velar region. 



