220 



THE PINEAL ORGAN 



Relation of the Pineal Organ to the Roof of the Skull in 

 Teleostean Fishes 



The tip of the end vesicle of the pineal organ may either simply 

 come in contact with the roof of the skull, or the whole superficial area 

 of an expanded vesicle may be in relation with the roof as in the gar- 

 pike (Fig. 155). Sometimes the stalk is so short that the end vesicle 

 does not reach the vault. It is only occasionally that the under surface 



Fig. 155. — The Parietal Region of the Brain and Pineal Organ of a Gar- 

 pike (Belone acus). Longitudinal Section. Adult Specimen, En- 

 larged. (After Reichert.) 



of the skull shows any depression for the reception of the end vesicle, 

 or a part of this ; such has, however, been observed by Cattie in the 

 common pike (Esox lucius) and in the Salmon (S. salar) ; also by Rabl 

 Riickhard (S. fario) and Hill {S. purpuratus). Cases in which a parietal 

 foramen closed superficially by fibrous membrane, is present either in 

 the cartilaginous or bony skull are exceptional. Handrick has, how- 

 ever, published figures of such in Argyropelecus hemigymnus, a species 

 of fish allied to the salmonoids and the herrings ; and Klinckostroem 

 has shown a true parietal foramen in the bony vault of the skull in 

 Callichthys asper, belonging to the cat-fish family. It is noteworthy, 

 however, that in this case, although a parietal foramen is present, the pineal 

 organ is not well developed. 



