218 



THE PINEAL ORGAN 





Fig 

 A : 



B. 



152. — The Pineal Organs of Corregonus albus. (After Charles Hill.) 



Dorsal view of embryo of Corregonus albus, showing the position of the 

 rudimentary epiphysis to the left of the median plane. 



Longitudinal section through the anterior and posterior epiphysis of a 7-mm. 

 embryo of C. albus. 

 C. : Transverse section through the posterior epiphysis of an embryo of C. albus ; 

 the arrow marks the median plane. 



Ant. Ep. 1 : Epiphysis I. Ol. PI. : olfactory placode. 



Cbl. : cerebellum. Op. V. : optic vesicle. 



Ep. 1 : anterior epiphysis. Post. Ep. 2 : Epiphysis II. 



Ep. 2 : posterior epiphysis. St. O. : static organ. 

 L. : lens. 



Hill considered that the posterior epiphyseal vesicle of teleosts and Amia is 

 homologous with the " epiphysis " of Lacertilia, and that the anterior vesicle 

 is homologous with the parietal eye of Lacertilia. 



The general structure of the pineal organ of the bony fishes is very 

 similar to that of the cartilaginous fishes, namely, a neuro-epithelium of 

 ependymal character, containing a few glial cells and cells resembling 

 nerve-cells, enclosed between two limiting membranes (Fig. 154). 

 Cytoplasmic processes frequently project through the internal limiting 

 membrane into the lumen of the organ. The vessels surrounding the 

 pineal organ form a rich anastomotic plexus, but they do not appear to 

 enter the epithelial walls. The end vesicle is never differentiated into an 

 eye-like structure, such as that of Petromyzon, although cells resembling 

 sensory-cells, unipolar nerve-cells, and ganglion-cells ending in nerve- 



