THE PINEAL SYSTEM OF FISHES 



213 



bow-fin. Its pineal organs were specially investigated by Hill (1894), 

 Eycleshymer and Davis (1897), an d Kingsbury (1897). Hill found that in 

 the early embryonic stages both parietal organs were present, there being 



aV^Post Ep 

 " or EpH 





^WMM\ 



S&i&y^Ac.Pn. 



(left Pn ; 0.) 



Fig. 149. — Drawings of Sections showing the Early Development of the 

 Epiphyses in Amia. (After Eycleshymer and Davis.) 



A — Sagittal section of primary vesicle of a larva 8-9 days old ; 5-6 mm. ; 160. 

 B — Transverse section through the epiphysis of a larva 10 days old ; 7-8 mm., 



showing the bifid cavity. 

 C — Transverse section through a larva at the same stage of development as B, 



and Fig. 150, C ; showing the right and left pineal organs, lying side by 



side. 

 D — Transverse section through a larva, 14-15 days old; 9-10 mm. at the same 



stage as Fig. 150, D, showing the right and left pineal organs. 

 E — Sagittal section of epiphysial region of larva 12-13 mm., showing fibre 



tract ft. lying in ventral portion of primary vesicle. 

 F — Section snowing nerve-fibres passing to the posterior epiphysis from the 



superior or habenular commissure. 



a larger posterior organ — which probably corresponds to the posterior or 

 right pineal organ of Petromyzon — and a smaller organ which lay in front 

 and to the left, which appears to be homologous with the anterior or left 

 parietal organ of Petromyzon or the " parapineal organ " of Studnicka. 

 In 10-mm. embryos the larger posterior pineal organ has developed into an 

 ovoid vesicle with a pointed anterior extremity. Its upper or distal wall 

 is convex and consists of a single layer of cells, while the lower wall has 

 three or four layers of nuclei. The vesicle is joined to the roof of the 

 diencephalon by a tubular stalk, which arises in the usual situation between 

 the habenular and posterior commissures. In older embryos the organ 

 rises perpendicularly from the brain and comes in contact with the 

 skin. The anterior parietal organ is situated close in front of and to 



